A sub-discipline of geography which studies the spatial relationships between humans and agriculture, as well as the cultural, political, and environmental processes that lead to parts of the Earth's surface being transformed into agricultural landscapes through primary sector activities.
A distinctly triangular or fan-shaped deposit of sediment transported by water, often referred to as alluvium. Alluvial fans usually form at the base of mountains, where high-velocity rivers or streams meet a relatively flat area and lose the energy needed to carry large quantities of sediment, which ultimately spreads out in all available directions. They tend to be larger and more obvious in arid regions.
A geographical location where there is little or no tide, i.e. where the tidal amplitude is zero or nearly zero because the height of sea level does not differ significantly at high tide and low tide, and around which a tidal crest circulates once per tidal period (approximately every 12 hours). The tidal amplitude increases, though not uniformly, with distance from these points. Amphidromic points are the consequence of resonance phenomena which occur when obstructing landmasses reflect tidal bulges back and forth across oceanic basins; their precise locations, usually in the open ocean near the center of the basin, depend largely on the surrounding topography and bathymetry, and also vary slightly with winds, currents, and the positions of the Sun and the Moon. There are at least a dozen well-defined amphidromic points across the Earth's oceans.
Also anastomosed stream.
A stream or river composed of multiple, branching, interconnected, coexisting channels that enclose floodbasins on alluvial plains, usually formed when a slow-moving river encounters avulsions that divert its flow, creating new channels on the floodplain.
The part of the Earth's surface which is uninhabited and/or uninhabitable by human beings. Contrast ecumene.
The steepest angle of descent or dip, relative to the horizontal plane, at which a mass of loose, freely movable material such as sand or unconsolidated rock debris can remain stationary, i.e. without sliding downward, despite the pull of gravity.
The southernmost of the Earth's two polar circles of latitude, south of which the sun appears above the horizon for 24 continuous hours at least once per year (and is therefore visible at midnight) and also appears at least partially below the horizon for 24 continuous hours at least once per year (and is therefore not visible at noon). Its latitude is approximately 66°33′47.1″ south of the Equator. Contrast Arctic Circle.
A stream or other watercourse that existed before the present form of the surrounding land surface was established and which maintains its original course and pattern despite changes in the local geology or topography. For example, a landscape featuring a river with a dendritic drainage pattern may be altered by gradual, localized tectonic uplift, but the river may be sufficiently powerful to erode through the new obstructions as rapidly as they are formed, carving a gorge rather than being redirected, and thereby preserving its dendritic pattern even though it now flows over a landscape that typically produces very different drainage patterns. Compare insequent stream.
1. The meridian of longitude that is directly opposite or antipodal to a given meridian, i.e. the imaginary line that is exactly 180 degrees of longitude distant from the given meridian. Together, a meridian and its antimeridian form a great circle that passes through the geographic poles.
2. The 180th meridian in particular, i.e. the meridian of longitude that is exactly 180 degrees both east and west of the Prime Meridian, with which it forms a great circle dividing the Earth into the Eastern and Western Hemispheres. The 180th meridian is used as the approximate basis for the International Date Line because it mostly passes through the open waters of the Pacific Ocean.
Any pair of points on the Earth's surface that are diametrically opposite to each other, such that a straight line connecting them would pass through the Earth's center. Such points are as far away from each other as possible, with the great-circle distance between them being approximately 20,000 kilometres (12,000 mi).
A geographic position which a GPS receiver is able to calculate without requiring information about its own location or the local time.
The apparent position of an object in space as seen by an observer, which, because of physical and geometric effects, may differ from the object's true position.
The application of geographical knowledge and techniques to the solution of economic and social problems on any scale, ranging from local to global, in disciplines such as civic planning, land use and management, location policy, and population studies, among many others.
A glacier resulting from the merging of two separate glaciers.
An underground layer of water-bearingpermeable rock, rock fractures, or unconsolidated materials such as gravel, sand, or silt, which is sufficiently porous to carry or conduct water yet also sufficiently coarse or non-absorptive to release the water and thereby permit its exposure to or access from the ground surface. Groundwater from aquifers may naturally emerge at the surface, e.g. at a spring, or may be extracted using man-made wells. There are many different types of aquifer with various levels of hydraulic conductivity.
The northernmost of the Earth's two polar circles of latitude, north of which the sun appears above the horizon for 24 continuous hours at least once per year (and is therefore visible at midnight) and also appears at least partially below the horizon for 24 continuous hours at least once per year (and is therefore not fully visible at noon). Its latitude is approximately 66°33′47.1″ north of the Equator. Contrast Antarctic Circle.
1. The sudden loss of land by the action of water.
2. The rapid abandonment by a river or stream of an existing channel in favor of the formation of a new channel, typically because the new channel follows a steeper or less obstructed course.
All of the locations of which an individual is "aware", i.e. about which they have knowledge above some minimum level, even those they may not have actually visited. Awareness space includes activity space, and it enlarges as new locations are discovered and new information is gathered. See also search space and mental map.
2. (of a fold) The imaginary central line or plane dividing the limbs of the fold as symmetrically as possible; the crest from which strata dip downward and away in an anticline, or the lowest depth of the trough from which strata rise in opposite directions in a syncline.
3. (of the Earth) The rotational axis of the Earth: the diameter between the North Geographic Pole and the South Geographic Pole, passing through the planet's geometric center, around which the Earth rotates anti-clockwise (i.e. to the east) once every 23 hours and 56 minutes. This axis is constantly tilted at an angle of about 66°30' with respect to the plane of the Earth's orbit around the Sun, which is the primary cause of the seasonal weather cycles experienced at temperate and polar latitudes.
The angle formed between a reference vector (often magnetic north) and a line from the observer to a point of interest projected perpendicularly to the zenith on the same plane as the reference vector. Azimuth is usually measured in degrees and can be determined with a compass.
A map projection in which all bearings are laid off correctly from the centerpoint of the map, so that all points on the map are true in distance and direction from the center.
The part of the profile of a hillslope that forms the steepest, typically linear portion of the slope, generally located in the middle and bounded by a convex shoulder above and a concave footslope below. The backslope may or may not include vertical or near-vertical cliffs.
The political fragmentation of a larger region or state into multiple smaller regions or states, often implying mutual hostility or lack of cooperation between such units, as has occurred frequently in the Balkan Peninsula of southeastern Europe.
2. An elevation in the bed of a river, stream, or shallow sea, either fully or partially submerged, mid-channel or connected to the shore, and usually made of sand, mud, gravel, or other loose sediment. See also bar and shoal.
The stage during which the channel of a river or stream is completely filled with water from bank to bank, immediately preceding the overbank stage, when the river overflows its banks and inundates the surrounding floodplain.
An impoundment built for seasonal floodwater storage and/or to create a reservoir for irrigation, as opposed to a dam, which instead serves the purpose of hydroelectric power generation, though at the broadest level the terms may be used more or less interchangeably.
A long, narrow ridge or shoal lying above the highest high tide level (thereby creating an island) and parallel to the mainland coast, from which it is separated by a lagoon. Barrier islands are analogous to very large sandbars deposited naturally by wave and tidal action, often in extensive chains along the coastline, but may also be created artificially by dredging. Though their size and shape change frequently, particularly during storms, they are important natural breakwaters which shelter areas of relatively calm waters where wetlands and marine life flourish. See also spit and tied island.
In the Spanish-speaking world, a neighborhood or community within a larger urban area, generally with informal boundaries, though in some places the term may refer to a formal subdivision of a municipality.
A coastal body of water that is directly connected to but recessed from a larger body of water, such as an ocean, sea, lake, or another bay. The land surrounding a bay usually shelters it from strong winds and waves, making bays ideal places for ports and harbors.
The direction or position of an object, or the direction of an object's movement, relative to a fixed point. It is typically measured in degrees and can be determined with a compass. By convention, magnetic north is defined as having a bearing of zero degrees.
A crevasse or series of parallel crevasses that opens in a glacier when a mass of moving ice detaches and pulls away from stagnant ice or firn. Bergschrunds are common in mountainous areas, often forming seasonally near the back of a cirque where the ice meets a steep or rocky headwall. When the rift forms directly between ice and rock, the gap is called a randkluft.
1. A level space, shelf, or raised barrier separating two areas, often man-made and built of compacted earth. Berms often function as impoundments, fortification lines, or border walls and other lines of demarcation.
2. A low, impermanent, nearly horizontal or landward-sloping shelf, bench, or narrow terrace on the backshore of a beach and parallel to the shoreline, formed by waves which deposit material beyond the average high water mark, e.g. during storms. Some beaches have no berms; others may have one or more.
The water of a slow-moving river channel flowing through a forested swamp or wetland, characterized by high concentrations of tannins leached from decaying vegetation, which results in a darkly stained color and high acidity.
A landscape of mixed woodland and pasture, with fields and winding country lanes sunken between low, narrow ridges and banks surmounted by tall, thick hedgerows, especially as found in rural parts of western Europe.
Any significant accumulation of water, either natural or artificial, on the surface of the Earth. Bodies of water may hold or contain water, as with lakes and oceans, or they may collect and move water from one place to another, as with rivers, streams, and other watercourses.
A type of wetland which accumulates deposits of dead plant material, especially mosses, known as peat. Bogs occur where the water at the ground surface is acidic and low in dissolved nutrients. They are one of four main types of wetland.
1. (tidal) A steep-fronted wave formed by the convergence of two tidal bulges or by the constriction of an incoming tide as it travels up a river, firth, or narrow bay, temporarily reversing the direction of the current.
2. (hole) A deep, man-made hole or shaft drilled into the ground, e.g. in mining, or for digging a well or tunnel.
A type of administrative subdivision in certain English-speaking parts of the world. Though traditionally used to refer to a fortress or a walled town, modern usage of the term can variably refer to any town with its own local self-government, a formal or informal subdivision of a large metropolis (as in New York City and London), or an entire administrative region (as in the U.S. state of Alaska).
Any line of demarcation, real or imaginary, visible or invisible, natural or artificial, with or without legal significance, which may be perceived from either or both sides of the line, indicating the place at which two or more geographical areas of distinct ownership, administration, legal jurisdiction, or any other quality meet; e.g. a border separating political or administrative divisions, zones of occupation, natural areas, or private and public property. See also frontier.
A region of a country or other polity which supports a large proportion of the country's domestic food production (especially of wheat and other grains) due to its fertile soils, favorable climate, and/or relative accessibility to agricultural interests.
1. Any more or less abrupt change in the profile of a slope, e.g. of a hillside.
2. A heavily eroded area along a river featuring steep banks, bluffs, ravines, or gorges. The term is used chiefly in the plural (i.e. breaks) and primarily in the United States and Canada.
A transfer point on a transport route where the mode of transport or type of carrier changes and where large-volume shipments are reduced in size. For example, goods may be unloaded from a ship and transferred to trucks at an ocean port.
Any man-made structure built on the coast of a body of water, typically the sea, in order to reduce the intensity of wave action in an area adjacent to the shore, thereby providing safe harbourage for human activities in the inshore waters. Breakwaters may also be designed to protect the coastline from coastal erosion and longshore drift.
Any previously developed area of land that is no longer in use, often with derelict buildings and infrastructure, in some contexts implying land that has been abandoned because of pollution or contamination.
An isolated hill or mountain with steep or precipitous sides, usually having a smaller summit area than a mesa.
1. A route which diverges around a place rather than traveling through it, especially a road or footpath built specifically for the purpose of diverting automobile or pedestrian traffic away from areas that are congested, blocked, under construction, or unsafe.
A type of parcel-based land recording system containing a comprehensive record of interests in individual units of land within a country or other polity, usually including a geometric description of each parcel's physical location, dimensions, and boundaries that is linked to legal information detailing the nature of the interests (e.g. rights, restrictions, and responsibilities), the ownership or control of those interests, and the economic value of the land and its improvements. The cadastre is a fundamental source of data used in resolving disputes between landowners.
A man-made stack or mound of rocks, stones, or masonry, usually roughly conical or pyramidal in shape, constructed as a burial mound, to mark a surveyed point, or as a landmark or waypoint to aid routefinding on a route that is otherwise unmarked and difficult to distinguish from the surrounding environment.
1. A primary city or town of a country, state, province, or other subnational polity, especially one that is a seat of government for the entire polity, either by law or by virtue of being the physical location of the government's offices and meeting places, or both. A capital is often but not always the largest or most economically or historically important city of its constituent. A polity may have one or more capitals, or none.
2. Any place considered to have informal primacy or importance with respect to some characteristic or association, e.g. Milan, Italy is sometimes unofficially called the "Fashion Capital of the World".
A map in which some thematic mapping variable, such as travel time, population, or gross national product, is substituted for traditional measures of land area or distance such that the geometry or space of the map is distorted in order to convey and emphasize the information of the alternate variable.
A track, road, or railway raised above a body of water or a low-lying place by virtue of being built upon a man-made embankment, typically constructed of earth, masonry, wood, or concrete. Compare bridge.
Either of the two imaginary points in the sky at which an indefinitely extended projection of the Earth's axis of rotation intersects the celestial sphere. As the Earth rotates upon its axis, the north and south celestial poles remain permanently fixed in the sky (directly overhead to observers at the North Pole and South Pole, respectively), and all other points appear to rotate around them.
The point in a geometric figure for which the coordinates are the average values of the coordinates of all other points in the figure, i.e. the arithmetic mean position of all points in the figure; or the point with the smallest possible average distance from all other points of the figure. In geography, the geographical center of a region of the Earth's surface is the centroid of the two-dimensional shape of that region, as projected radially to sea level or onto a geoid.
A unit of length equal to 66 feet (20.117 m), used especially in public land surveys in the United States; 10 square chains is equal to 1 acre (0.40 hectares). Though the literal chains used to measure this distance have long been superseded, surveying tapes are often still called "chains", and measuring with a tape may be called "chaining".
A warm, dry wind experienced along the eastern side of the Rocky Mountains in the United States and Canada. Most common in winter and spring, it can result in a rise in temperature of 20 °C (36 °F) in a quarter of an hour.
A sovereign state or small independent country that usually consists of a single city and its dependent territories.
1. The practice of permanently removing vegetation, especially trees and bushes, from a forest or woodland in order to use the space for another purpose, such as agriculture, civic development, or paths for roads, railways, or power lines.
The vegetation that would exist in an area if growth had proceeded undisturbed for an extended period. This would be the "final" collection of plant types that presumably would remain forever, or until the stable conditions were somehow disturbed.
A territory under the immediate complete political control of a sovereign metropolitan state but otherwise distinct, often geographically, from the state's home territory. Colonies have no international representation independent of the metropolitan state. Compare satellite state.
A steep, narrow valley or a large hollow on the side of a hill or coastline, especially one enclosed on all but one side. The term is used primarily in southern England, where it often implies a dry ravine in a limestone or chalk escarpment. See also cwm.
One of several very large, contiguous landmasses into which the Earth's land area is divided, generally by geographical or political convention rather than any strict criteria. Geologically, continents correspond largely to areas of continental crust on continental plates.
The type of climate found in the interior of the major continents in the middle or temperate latitudes. The climate is characterized by a great seasonal variation in temperatures, four distinct seasons, and a relatively small annual precipitation.
The line of high ground that separates the different oceanic drainage basins of a particular continent. The river systems of a continent on opposite sides of a continental divide flow toward different oceans. See drainage divide.
A portion of a continent that is submerged beneath an area of relatively shallow water known as a shelf sea. Though continental shelves are usually treated as physiographic provinces of the ocean, they are not part of the deep ocean basin proper but the flooded margins of the continent.
A line marked on a topographic map which connects points of equal elevation above or below a specified reference datum. Multiple contour lines, each representing a different elevation, are depicted together to show the shape of the terrain within the map area.
A long chain of mountain ranges or highlands, especially those formed by the same orogeny and spanning the length of a continent along tectonic boundaries. The term is used in particular to refer to the American Cordillera, an almost continuous system of parallel ranges lining the west coasts of North, Central, and South America.
The portion of a country or territory that contains its economic, political, intellectual, and cultural focus. It is often the center of creativity and change. See also hearth.
The cardinal direction in which a vessel or aircraft is moving, or in which it is steered. This is not necessarily the same as the heading, the direction in which the craft's bow or nose is pointed; any difference between heading and course is due to the motion of the air or water through which the vessel is moving, or other aerodynamic effects such as skidding or slipping. See also bearing.
An old and stable region of continentallithosphere, characterized by a thick crust composed of ancient crystalline basement rock. Cratons are generally found in the interiors of tectonic plates, having remained relatively unaffected by orogenic and tectonic activity for very long periods of time.
The thin shell of solid material that is the Earth's outermost layer and the outermost component of the lithosphere. The Earth's crust is generally divided into two distinct types, oceanic crust and continental crust, both of which "float" on top of the mantle.
The totality of water in the solid phase on the Earth's surface, including glaciers; sea, lake, and river ice; snow; and permafrost. The cryosphere is sometimes considered a subset of the hydrosphere.
A tunnel or conduit that channels water through or beneath an obstacle (e.g. through a man-made crossing of a ravine that would otherwise block the natural flow of water), or any artificially buried watercourse.
An arc-shaped, dune-like mound of sediment on a beach or foreshore. Cusps tend to be uniformly spaced in repeating patterns close to the shoreline, with the embayment of each arc made of fine-grained sand or gravel and the "horns" made of coarser sediment.
A continually erodingbank along a meandering river or streamchannel, especially a bank that has been eroded into a nearly vertical cliff. Cut banks generally form on the outside bend of a deep meander, opposite the depositional point bar that forms on the inside bend.
Any barrier, either natural or artificial, that stops or restricts the flow of water, either on the surface or underground. Man-made dams are most commonly built to impound rivers or streams, generally to retain water for purposes such as human consumption, irrigation, aquaculture, or power generation (whereas related structures such as floodgates and levees are more specifically designed to manage or prevent water flow into particular areas).
A type of thematic map that uses areal symbols to visualize a spatially dependent variable (e.g. population density) by refining a choropleth map with ancillary information about the distribution of the variable. The dasymetric method attempts to improve the resolution of maps based on average or per-capita figures calculated for discrete administrative units, which tend to show sharp contrasts between adjacent areas, by supplementing these figures with additional geographic data that allow more precise categories to be constructed. Dasymetric maps are a hybrid of choropleth and isarithmic maps, combining their strengths and weaknesses in order to more accurately depict quantities that vary continuously across space.
A place where water runoff from a relatively small, confined space emerges into a much larger, broader space, or where a body of water pours forth from a narrow opening, such as where a stream or river enters a lake or ocean.
A unit of angular measure, represented by the º symbol. A circle is divided into 360 degrees; subdivisions of the degree include the minute (1⁄60 of one degree) and the second (1⁄3600 of one degree). Degrees are commonly used to divide the roughly spherical shape of the Earth for geographic and cartographic purposes, e.g. when reporting latitudes and longitudes.
A landform at the mouth of a river where the main stem splits up into several distributaries. It is formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Compare estuary.
A territory relying on or subject to the control of another country, neither possessing full political independence nor forming an integral part of the controlling country's political or economic interests.
Any natural process by which material such as soil and rocks is added to a landform or landmass, e.g. by the action of wind, water, ice, or gravity in transporting previously weathered surface material, which comes to rest when sufficient kinetic energy is lost and accumulates in layers of sediment. See also sedimentation.
An area of land which has been damaged or devalued by some process, either natural or man-made (e.g. extractive industry), and/or simply neglected, causing it to be abandoned by human interests (and often other organisms) and leaving it incapable of being used productively in its present condition. See also brownfield land.
An arid, barren area of land where little precipitation occurs and living conditions are consequently unfavorable for most plant and animal life. Deserts are characterized by exposure of the unprotected ground surface to processes of denudation as well as large variations in temperature between night and day. They are often classified by the amount of precipitation they receive, by their average temperature, by the causes of their desertification, or by their geographical location.
A ground surface, often found in arid environments, covered with interlocking rock fragments of pebble and cobble size, closely packed after the removal of finer rock material and smoothed or polished by blown sand so that eventually their upper surfaces are more or less uniformly flat.
A conspicuous orange-yellow to black coating often present on exposed rock surfaces in arid environments, consisting of thin, hard, polished layers of metal oxides, especially iron and manganese, which form when minute quantities of matter migrate to the surface of the rock by capillary action and are then precipitated by evaporation.
The process by which a previously fertile area becomes increasingly arid, infertile, or desert-like; a type of land degradation in which biological productivity is lost due either to natural or man-made processes, e.g. climate change or overexploitation of soils for agriculture.
A straight line drawn on a map between the point of origin and the destination of a trip, i.e. the shortest distance between these two points, indicating the route a person would like or desire to follow if it were possible.
Any path or trail, often a footpath, created as a consequence of erosion caused by human or animal traffic, usually representing the shortest or easiest route to navigate between an origin and a destination. Desire paths often emerge as shortcuts where constructed paths or roads are circuitous, have gaps, or are non-existent.
A shallow artificial pond built to capture and hold rainwater or sea mist in order to water livestock, made especially in areas where natural supplies of surface water are not readily available, such as on the chalk downlands of southern England.
1. A ditch, wall, embankment, or ridge, natural or man-made, that is an obstacle to something else; another name for a levee.
2. In geology, an intrusion in which molten rock has ascended through an approximately vertical fissure and solidified into a wall of rock that is often harder or less permeable than the rocks of the surrounding strata.
In hydrology, the volumetric flow rate of water through a particular cross-sectional area, i.e. the volume of water that passes a particular point along a waterway (e.g. a cross-section of a streamchannel) per unit time. The measure includes the volumes of any suspended solids, dissolved chemicals, or organic matter in addition to the water itself. Discharge is commonly measured for both natural and man-made hydrological systems, where it may be referred to by various names including streamflow and outflow.
A landscape produced by significant stream erosion and incision of a plateau such that only a small part of the plateau surface is at or near the original elevation of the summit; much of the area instead occurs as eroded hills or badlands.
The decrease in cultural or spatial interactions between two places as the distance between them increases. This effect may be noticeable in towns and cities, where certain characteristics such as pedestrian traffic, building height, and land value tend to decline with greater distance from the city center.
A type of administrative subdivision used by governments and institutions worldwide, typically at regional or local levels. Districts are commonly drawn to define the jurisdictions of special local government services, such as law enforcement and education, and often function more or less independently of the municipal or county governments that designate them. The term can refer to a wide variety of official and colloquial subdivisions, including electoral districts, school districts, and shopping districts.
2. An uplifted area of sedimentary rock with a downward dip in all directions, often caused by molten rock material pushing upward from below. The sediments have often eroded away, exposing the rocks that resulted when the molten material cooled.
In southern Africa, another name for a gully or badland carved by extreme erosion.
An open, treeless expanse of gently undulating, elevated grassland, usually of chalk and supporting grazing for livestock. The term is used primarily in southern England, Australia, and New Zealand.
The natural or artificial removal of surface and/or sub-surface water from an area with excess water, e.g. via runoff facilitated by channels such as streams and rivers, into which water collects and is transported to sea level by gravity. The patterns, hierarchies, and evolution of drainage networks are widely studied in physical geography disciplines.
1. A terrain feature formed by two parallel ridges or spurs with low ground in between them.
2. Another name for an arroyo, ravine, or gulch, especially one with a broad floor and gently sloping sides.
The maximum extent to which the water table is reduced in elevation as a result of pumping water from a well that penetrates an aquifer. The amount of draw down diminishes logarithmically with distance from the site of the well, a fact which determines the shape of the subsurface cone of depression in the area surrounding the well.
A type of farming practiced in semi-arid or dry grassland areas without irrigation, instead using such approaches as fallowing, maintaining a finely broken surface, and growing drought-tolerant crops.
An ecoregion or more generally any land area defined by a relative scarcity of water, where precipitation is evenly balanced or exceeded by evaporation from surfaces and evapotranspiration by plants. Drylands encompass all sub-humid and arid environments, from tropical savannas to hyper-arid extremes such as deserts.
1. A collective term for the various fields of natural science related to the planet Earth.
2. The branch of science that studies the physical constitution and characteristics of the Earth and its atmosphere, using methods and tools from geography, geology, physics, chemistry, biology, and mathematics to build a quantitative understanding of how the Earth works and changes over time.
A type of biogeographic province that is smaller than a bioregion and which contains characteristic, ecologically and geographically distinct, and relatively uniform assemblages of biological communities and species. Ecoregion boundaries often overlap within ecotones and mosaic habitats, and most ecoregions contain habitats that differ from those described for their assigned biome.
A transition area between two biological communities, where different communities meet and integrate. It may manifest as a gradual blending of the communities across a broad area, or as an abrupt boundary line.
1. The habitable world according to the ancient Greeks; the part of the Earth's surface that is suitable for permanent human settlement, e.g. because it is climatically tolerable and physically occupiable.
2. All of human civilization considered collectively.
The transitional areas of "fringe" space at the boundaries of a country, city, or other artificial geographical entity, often distinguished by a partly man-made, partly natural landscape that is in the earliest stages of human management and organization. Compare hinterland.
The extent to which a place or service is actually accessible, governed not only by the distance to be traveled but also by whether or not the means of transport, the time available, and social circumstances make access possible.
The scientific study of human settlements of all types, incorporating concepts such as regional, metropolitan, and community planning and dwelling design with the goal of achieving harmony between the inhabitants of a settlement and their physical, social, and cultural environments.
1. The height of a geographic location above or below a fixed reference point; in particular, the height of a point on the Earth's surface with respect to sea level (or at least to a referencegeoid used as an approximation of the Earth's mean sea level). Compare altitude, geopotential height, and depth.
2. The vertical angle between the horizontal and a high point, e.g. between the horizon and a star in the night sky, or between the base of a mountain and its summit.
3. In architecture, a view of one of the sides of a building, or a drawing of this view.
A tract or territory completely surrounded by and enclosed within the territory of exactly one other state, country, or other political entity. Unlike enclaves, exclaves can be surrounded by more than one other state.
A place (e.g. a port, city, or trading post) to which physical goods or merchandise are brought to be stored temporarily while awaiting export to another country, and where they are not liable to customs duties. Though the term once described important commercial centers situated along long-distance trade routes, modern customs areas have largely made such entrepôts obsolete, and the term is now more commonly used to refer to duty-free ports with a high volume of re-export trade.
The imaginary great circle around the Earth halfway between the geographic poles which is assigned a latitude of zero degrees and therefore used as a reference point for all other lines of latitude. It is the largest circumference of the Earth.
A plain beneath which the bedrock has been subjected to considerable subsurface weathering, known as "etching". Erosion of the regolith overlying an etchplain often exposes topographical irregularities such as inselbergs.
A portion of a state or territory that is geographically separated from the main part by surrounding foreign territory of one or more other states or political entities. Many exclaves are also enclaves.
A stream found in an area that is too dry to have spawned such a flow. The flow originates in some moister section.
A selected point in a projected coordinate system from which the position of any place can be expressed in terms of its coordinates with respect to the selected point. The false origin differs from the true origin in order to exclude negative values.
An area of spongy, waterlogged ground containing decaying vegetation that accumulates over time into peat, and which is supplied with an input of mineral-rich surface or groundwater and thereby directly connected to a larger hydrological system. This external input typically results in higher mineral concentrations and a more alkaline pH than other peat-forming ecosystems such as bogs. Fens are one of four main types of wetland, along with bogs, marshes and swamps.
1. Any large, open outdoor space, natural or man-made, especially one with a natural surface covering such as grass or soil and having few trees and structures, permitting long sightlines.
2. (variable) A property, quantity, or observation (e.g. temperature, soil moisture, population density, etc.) that can be theoretically assigned to any point of space and which varies across space. Both scalar and vector fields are found in GIS applications, although the former is more common. Also spatially dependent variable.
The size and shape of the Earth as studied in geodesy. Applications requiring varying levels of precision have led to the development of many different models of the Earth, ranging from simple spheres to much more accurate approximations such as geoids.
A type of ice that is at an intermediate stage between snow and glacial ice. More specifically, firn is partially compacted névé left over from past seasons which has subsequently recrystallized into a form that is harder and denser than névé.
A colloquial term loosely applied to the topographically lowest step of a floodplain that experiences regular flooding, i.e. the first part to be inundated when a flood occurs, though the frequency considered "regular" is inconsistently specified. The term is used primarily in the Midwestern United States.
Another name for a coastal inlet, strait, or bay associated with the mouth of a large river, where the tidal effects of seawater passing upriver have widened the riverbed into an estuary. The term is used primarily in Scotland.
A primarily vertical artificial barrier designed to temporarily contain the waters of a river or other waterway which may rise to high levels during flooding events. Flood walls are narrower and typically easier to build than dikes or levees, so they are mainly used in locations where space is limited or where building more traditional flood-control structures would interfere with other interests.
2. A large-capacity channel or culvert designed to capture and divert floodwaters or excess streamflow from populous or flood-prone areas and eventually drain it into a river or other body of water, e.g. an artificial drainage canal bounded by levees. They often run below street level in larger cities.
3. A road crossing of a flood-prone channel, built at or close to the natural ground level. It is similar to a causeway but crosses a shallow and often dry depression that is subject to flooding, rather than a continuously flooded waterway.
4. A part of a floodplain kept clear of encumbrances and reserved for emergency diversion of floodwaters.
A glacial landform created by the movement of a glacier around a boulder, consisting of a lineation or streamlined furrow or ridge parallel to the direction of ice movement. They generally form in newly deposited till or older drift and can reach heights of 25 metres (82 ft) and lengths of 20 kilometres (12 mi).
The characteristic of a place that follows from its interconnections with more than one other place. When interaction within a region comes together at a single place (i.e. when the movement focuses on that location), the place is said to possess focality.
A geographic transition zone defined by gradual increases in elevation between plains or low-relief hills and adjacent topographically higher hills, mountains, or uplands.
The part of the profile of a hillslope that forms the concave surface at the base of the slope. It is a transition area between sites of erosion and transport higher up the slope (e.g. the shoulder and backslope) and sites of deposition further down the slope (the toeslope).
A place, natural or man-made, where a river or stream is shallow enough to be crossed by wading, or by getting a vehicle's wheels wet (as opposed to crossing a permanently dry bridge). Fords may be seasonal or temporary, becoming impassable during high water.
A relatively narrow, deep, elongated, and steep-sided trough in the ocean floor, usually near or parallel to a mountainous land area or associated with an archipelago, or such a trough when infilled with sediment. See also foreland basin.
1. Any land area or territory located in front of something else.
2. A landform projecting into the sea, e.g. a cape or headland.
3. The seaward trading area associated with a particular port or harbor.
A geographical dictionary or directory used in conjunction with a map or atlas and containing information concerning the geographical make-up, social statistics, and physical features of a country, region, or continent.
A coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters, or symbols. Geographic coordinates are often chosen such that one of the numbers represents a vertical position such as elevation and two or three other numbers represent a horizontal position such as latitude and longitude.
A digital public-domain database developed by the U.S. Geological Survey and the U.S. Board on Geographic Names which contains name and locative information about more than two million physical and cultural features located throughout the United States and its territories. Each feature recorded in the database receives a unique feature record identifier called a GNIS identifier.
Also geographical momentum.
The tendency of a place with established installations and services to maintain its size and its importance as a focus of economic or industrial activity after the conditions originally influencing its development have appreciably altered, ceased to be relevant, or disappeared.
A unit of length defined as the distance equal to one minute of arc along the Earth's Equator: approximately 1,855.3 metres (1.1528 mi; 1.8553 km). The precise length varies with the reference ellipsoid used to approximate the shape of the Earth. Regardless of the particular ellipsoid, the length of one degree of longitude at the Equator is equal to exactly 60 geographical miles.
The shape that the surface of the Earth's oceans would take under the influence of Earth's gravity and rotational acceleration alone, in the absence of other influences such as winds and tides. It is often characterized as the precise mathematical figure of the Earth: a smooth but irregular gravitational equipotential surface at every point of which, by definition, the direction of the force of gravity is always perpendicular and spirit levels are always parallel. Its shape results from anomalies in the Earth's gravitational field caused by the uneven distribution of mass within and on the Earth's surface. A reference ellipsoid is an idealized approximation of the more complex and accurate geoid.
The identification or estimation of the real-world geographic location of an object, involving the generation of a set of geographic coordinates in order to determine a more meaningful description of location, such as a street address.
A section of a city occupied by members of a minority group who live there because of social restrictions on their residential choices. Originally, the term referred specifically to a section of a European city to which Jews were confined.
A deserted or abandoned village, town, or city, especially one in which remaining buildings and infrastructure such as roads are still visible. The term is also sometimes used to refer to settlements that are still populated, but significantly less so than in previous years.
A persistent mass of dense ice that is constantly moving under its own weight, and which is composed largely of compacted snow that forms where the annual accumulation of snow exceeds its melting and sublimation over very long periods of time. Glaciers slowly deform and abrade the land beneath them, creating a huge variety of landforms including cirques, moraines, and fjords. They form exclusively on land and are distinct from the much thinner ice that forms on bodies of water.
A city which functions as an important or primary node in the global economy. Though criteria are not strictly defined, a global city typically is very large; dominates trade and economic interactions within a large surrounding area; supports a large and demographically diverse population; serves as a center of ideas and innovation in business, science, culture, and politics; and/or is a headquarters for major financial institutions, multinational corporations, or worldwide media and communications networks.
The process of interaction and integration among people, companies, governments, and cultures across the world. A complex and multifaceted phenomenon, globalization is considered largely the result of economically motivated advances in transportation and communication technologies in the past several centuries which have dramatically increased interactions between otherwise isolated groups of people.
A depression or valley bounded on either side by distinct, parallel escarpments or faults and formed by the downward displacement of a block of the Earth's crust. Grabens often occur side-by-side with horsts, their uplifted or non-displaced counterparts, in a repeated series of vertical displacements.
Also slope, incline, gradient, pitch, rise, or mainfall.
A physical surface that is inclined with respect to the horizontal, or the angle between that surface and the horizontal, typically expressed in degrees, or calculated as a ratio of "rise" (vertical distance) to "run" (horizontal distance) and expressed as a fraction or percentage; a larger number indicates a steeper incline. The term "grade" is often used to describe the incline of man-made surfaces such as roads and the roofs of buildings, whereas the term "slope" is more commonly used to describe natural surfaces such as the sides of hills or mountains or the beds and banks of watercourses.
Any land area where the vegetation is dominated by grasses (i.e. plants of the botanical family Poaceae), sometimes also inclusive of grass-like plants of other families. A large and important biome occurring worldwide, grasslands may be natural or created for agricultural purposes.
The measurement of the strength of a gravitational field, especially the Earth's gravitational field, typically by calculating the acceleration due to gravity at a particular point on the Earth's surface. Because it can vary widely across the surface, knowing the local magnitude of the gravitational force is often necessary in order to produce accurate geographical data.
Any circle on the surface of a sphere created by the intersection of the sphere and a plane that passes through its center. A great circle divides the sphere into two equal hemispheres, and all of a sphere's great circles have the same center and circumference as each other, which by definition is the largest possible circumference of the sphere. The mathematical properties of great circles make them useful in geodesy, where they are often visualized upon the surface of the Earth (despite the fact that the Earth is not a perfect sphere): for example, the Equator of the idealized Earth is a great circle, and any meridian with its antimeridian forms a great circle. Because the shortest path between any two points on the surface of a sphere follows the arc of a great circle, great-circle distances are often used as approximations of geodesics for the purposes of air and sea navigation.
The horizontal direction or bearing followed by the arc of a great circle through a given pair of terrestrial points, expressed as the angular distance from a reference direction.
The length of a line between two points which follows the arc of a great circle as defined by the intersection of the Earth's surface with an imaginary plane passing through the Earth's center. It is the shortest route between those two points on the Earth's surface.
A special land-use zone designated in some cities to prevent development of wild, largely undeveloped, or agricultural land surrounding or adjacent to urban areas, in order to conserve natural ecosystems, to allow the return and establishment of wildlife, and/or to create urban green space for aesthetic or recreational purposes. The term may also refer more specifically to the boundary between developed and undeveloped areas rather than to the undeveloped area itself.
The part of the year during which local weather conditions (i.e. temperature and precipitation) permit the normal growth of plants in a given location. What defines a "growing season" is often informal and colloquial, and may vary widely by location and from year to year; in many places, the local growing season is defined as the period of time between the average date of the last frost (in temperate parts of the Northern Hemisphere, this typically occurs in the spring) to the average date of the first frost (in the autumn).
A device consisting of a spinning disc or rotor mounted in such a way as to preserve the orientation and angular velocity of its axis of rotation with respect to an inertial reference frame, irrespective of perturbations to the mounting itself, which makes it possible to measure and maintain an unbiased equilibrium in the attitude and/or course of a moving object such as an airborne or waterborne vehicle or camera. Modern digital gyroscopes and their associated supporting readouts are widely used in navigation and geodesy as the basic sensor in direction-seeking, direction-keeping, and attitude stabilization systems.
An individual's sense of "home", or of their place in the world, comprising socially ingrained habits, beliefs, skills, and dispositions based on their geographical environment, cultural origin, inheritance, experiences, and the social networks they develop throughout their life, all of which may be subject to refashioning with passing time or increasing distance.
Any of a series of non-numerical lines used on a map to indicate the general orientation and steepness of topographicalterrain. Such lines vary in length, thickness, and spacing, with steeper slopes indicated by shorter, heavier, and more closely spaced lines.
In the context of geography, the detrimental effect of a border or other boundary on locations close to it, making those locations unattractive to people intending to visit or settle there; e.g. a political boundary in disputed territory, where immigration across the boundary occurs frequently. There may also be beneficial effects on such locations.
In southern England, a plot of meadow land, especially a tract of rich pasture near a river; or a small settlement, ranging in size from a single homestead to a town.
A desert landscape consisting of high, largely barren, rocky plateaus where most of the sand has been removed by deflation, and thus lacking most surficial materials other than boulders and exposed bedrock.
A tributaryvalley that is higher in elevation than the main valley into which it drains, such that it appears to be "hanging" above the lower valley. Hanging valleys are commonly the result of differential glacial erosion, when adjacent areas beneath a glacier are subjected to different rates of erosion.
The compassdirection in which the bow or nose of a moving vessel or aircraft is pointed. This is not necessarily the same direction in which the vessel is actually traveling, known as its course; any difference between heading and course is due to the motion of the air or water through which the vessel is moving, or other aerodynamic effects such as skidding or slipping. See also bearing.
1. Another name for the source of a river, stream, or other watercourse, i.e. the point or points furthest from the mouth of a particular stream, at which precipitation, meltwater, or groundwater first accumulates into a persistent, identifiable, and/or named body of water whose contents ultimately empty into the particular stream; or all of the uppermost streams of a watershed considered collectively (of which there may be thousands), typically including all streams identified as first-order through third-order in conventional stream order systems.
2. The entire region, inclusive of land, surrounding these sources, often abutting the boundary of a drainage divide that separates different watersheds.
A natural or man-made demarcation that indicates the maximum rise of a body of water over land. Though not necessarily an actual physical mark, river or sea waters rising to a high point often leave a lasting physical impression such as a noticeable discoloration or deposition of debris; such a mark is often the result of a flood or storm surge. High water marks may reflect an all-time high, an annual high, or the high point for some other division of time (e.g. a tidal cycle). A natural delineation created by debris deposited by a high tide is called a strandline. See also wash margin and mean high water.
2. Any area of land (mountainous or otherwise) that is higher in elevation relative to another area. In this sense, the term is often used as a conditional descriptor to distinguish related habitats or ecosystems, especially freshwater riparian areas, on the basis of elevation above sea level.
A branch of human geography that studies the ways in which geographic phenomena have changed over time, especially (though not necessarily limited to) geographic change as it relates to human activity; the geography of the past, whether real, perceived, or theoretical.
A projecting ridge or outcropping of land, its height ending abruptly or steeply. The term is used primarily in placenames in Great Britain.
A long, narrow ridge or series of hills with a narrow crest and steep, symmetrical slopes of nearly equal inclination on both flanks, especially one created by the differential erosion of an outcropping which exposes homoclinal sedimentary rock strata. Compare esker, drumlin, and cuesta.
Aerial view of a hogback in the southwestern United States
Land owned or occupied by legal right for the purpose of agriculture.
1. (dwelling) A house or home, especially an isolated farmhouse with its associated outbuildings on a large agricultural holding such as a ranch; or a small rural settlement of dispersed farms.
2. (legal concept) In the United States, a plot of land given legal meaning by a series of federal laws granting applicants ownership of land in the public domain upon the condition that they live on it and improve it. Homesteaders were initially granted plots of 160 acres (0.65 km2), which was considered adequate to support a single family, but later as much as 640 acres (2.6 km2).
The apparent line that separates the ground from the sky, dividing all visible directions into two categories: those that intersect the Earth's surface and those that do not. When not obscured by buildings, trees, or mountains, the true horizon can be useful in navigation and determining positional orientation. In perfect visibility, to an observer on Earth standing at an elevation of 3 metres (10 ft) from the horizontal, the horizon in any direction is approximately 6.5 kilometres (4 mi) distant; at 30 metres (100 ft), it is 21 kilometres (13 mi) away.
The distance between two points on a land surface when projected on to a perfectly horizontal (i.e. flat) plane, e.g. on a map, as opposed to measuring the actual physical length along the real-world surface, which can be greatly increased by slopes and other topographic variations. The distance between the start and end points of any route, even if at the same elevation, will often appear to be much shorter on a map than the shortest route that could actually be walked between them, because of the influence of real-world changes in vertical displacement along the path followed by the route.
A mountain formed by the back-to-back abutment of three or four adjacent cirques, leaving a distinctly pyramidal peak.
A raised block of the Earth's crust, bounded by parallel escarpments or faults, that has been displaced upward or has remained stationary while adjacent blocks on either side, known as grabens, have been displaced downward. Horsts and grabens often occur side-by-side in a repeated series of vertical displacements.
The branch of geography that studies humans and their communities, cultures, economies, and interactions with the environment by examining their relations with and across space and place. Along with physical geography, it is one of the two major sub-fields of geography.
Also humanist geography.
An approach in human geography which emphasizes the subjective as distinct from the objective in that it stresses the importance of perception, creativity, thinking, and beliefs as well as human experience and values in the formation of the attitudes of people toward their environment and in affecting their relationships with it.
A graph showing the rate of flow (i.e. the discharge) of water past a specific point of measurement in a river or other channel over time, typically expressed in cubic metres or cubic feet per second (m3 or ft3/s).
The totality of the water found on, under, and above the Earth's surface in liquid, solid, and gaseous forms, including all oceans, lakes, rivers, and streams, as well as all ice and glaciers and subsurface groundwater. Some definitions restrict the hydrosphere to liquid water only, instead placing solid forms in the cryosphere and gaseous forms in the atmosphere.
Any very long period of Earth's history during which surface and atmospheric temperatures are greatly reduced, resulting in the development or expansion of continental and polar ice sheets and widespread glaciation. The most recent such period was the Pleistocene Epoch, which ended approximately 12,000 years ago.
A flattened, often dome-shaped mass of ice that covers less than 50,000 square kilometres (19,000 sq mi) of land area and is not constrained by topographical features such as mountains; larger masses of ice are termed ice sheets. Contrast polar ice cap.
A mass of glacial ice that covers more than 50,000 square kilometres (19,000 sq mi) of land area; smaller masses of ice may be termed ice caps or ice shelves. The two polar ice sheets are the only ice sheets that currently exist on Earth.
A large floating platform of ice formed when a glacier or ice sheet in a coastal area flows onto the ocean surface. By contrast, sea ice is formed directly over the water and is typically much thinner.
A region of relatively fast-moving ice within an ice sheet that flows like a stream under its own weight (making it essentially equivalent to a glacier) and empties into the ocean. Ice streams are responsible for the majority of the mass lost from both the Antarctic and Greenland ice sheets.
A portion of a glacier where a steepening or narrowing of the underlying bed causes the ice to move more rapidly than elsewhere, resulting in a chaotic, highly fractured surface characterized by numerous crevasses and seracs.
A type of crater formed by the hypervelocity collision of a solid astronomical body, such as a meteor, with the Earth's surface. Unlike volcanic craters, impact craters typically have raised rims higher in elevation and depressed floors lower in elevation than the surrounding terrain.
Any land area which has been intentionally altered from its natural condition by human activity, such as ploughing, clearing, cultivation, or some other form of management, and thereby made more valuable or productive for human purposes (not necessarily to the benefit of any other organism or the environment in general). Legal definitions vary with location, but in most countries the term refers primarily to certain types of agricultural land or to property which has been developed for residential or commercial use.
Also clinometer, declinometer, tilt meter, gradient meter, slope gauge, and level gauge.
An instrument used to measure angles of slope, elevation, or depression with respect to the direction of the gravitational force, i.e. in the vertical plane, including both inclines and declines. The measure may be expressed in degrees, percentage points, or topos.
A contour line drawn with a heavier line weight to distinguish it from intermediate contours. Depending on the contour interval, index contours are usually indicated every fourth or fifth contour, along with their assigned numerical values, in order to facilitate ease of interpretation.
inertia costs of location
Costs borne by an activity because it remains located at its original site, even though the distributions of supply and demand have changed.
The broad set of facilities and interrelated systems that serve a city, country, or any other inhabited area, encompassing the structures and services necessary for its industries, economies, and residential spaces to function, i.e. for the human population occupying these spaces to get what they want or need when they want or need it. Infrastructure may include public and private physical structures such as roads, railways, bridges, tunnels, water reservoirs, canals, sewers, and electrical and telecommunications networks, among other things. A well-developed infrastructure is essential to enable, sustain, and improve living and working conditions in any society or organization.
A generally flat coastline whose shape has been largely defined by the penetration of the sea into relatively low-lying areas of the land surface, often as a result of crustal movements or a rise in sea level, such that the boundary between land and water closely matches the topographic contours of the land prior to its being covered by seawater.
A subsection of a map that is reserved for depicting another map of the same place at a different scale, often a smaller scale to show relative location within a larger geographic area (e.g. a country's location on the globe) or a larger scale to show increased detail (e.g. of public transit routes in a downtown area), or with different features or overlays in order to provide additional information that would be difficult to interpret if presented in the main map area. Insets are usually outlined with an obvious boundary to prevent confusion, and may include their own set of cartographic elements such as a scale, graticule, and legend.
Of or relating to an island, or suggestive of the isolated condition of an island.
A drainage pattern in which stream systems have developed to the point that all parts of the landscape drain into some part of a stream and to a common base level, the initial or original surfaces having essentially eroded away entirely, such that few or no closeddrainage systems are present.
Any place where the contiguous geographic area represented in a map projection has been split, separating to distant parts of the projection certain features and locations which are in reality much closer to each other, in order to permit the representation of a three-dimensional space on a two-dimensional map. All world maps, for example, have at least one interruption, conventionally along the length of a single meridian, thus forming an east–west boundary despite that the approximately spherical shape of the Earth is continuous, with no such boundaries; features on either side of the interruption, though very close to each other on the actual Earth, are depicted on opposite edges of the map, appearing to be separated by thousands of miles. Some world map projections attempt to reduce distortion of scale by having more than one interruption, which divide the projected area into multiple gores, each with its own central meridian.
The existence of a closer, less expensive opportunity for obtaining a good or service, or for a migration destination. Such opportunities lessen the attractiveness of more distant places.
A system of navigable inland waterway channels, maintained through dredging and sheltered for the most part by a series of linear offshore islands, that follows the Atlantic and Gulf Coasts of the United States more than 4,800 kilometres (3,000 mi) from Boston, Massachusetts, around the southern tip of Florida, to Brownsville, Texas.
Any line on a map connecting places of equal value of some specified variable. The variable may be a physical or natural quantity, such as elevation above sea level (as with contour lines) or temperature (as with isotherms), or a quantity related to social or economic statistics, such as population, wealth, or transport costs.
The state of gravitational equilibrium between the Earth's crust and its mantle, such that the crust "floats" at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earth's surface. Isostatic theory maintains that where equilibrium exists at the surface, equal mass must underlie equal surface area, and that the thickness of crustal features and the depth of the world's oceans tend to change over time in order to compensate for the uneven distribution of mass in the lithosphere. For example, the instability of continental margins where high mountains are found adjacent to deep oceanic trenches is explained by the subterranean movement of magma to effect a return to regional equilibrium, a process known as isostatic adjustment.
An irregularly shaped hill or mound composed of sand, gravel, and glacial till which accumulates in a depression on a retreating glacier and is subsequently deposited on the land surface with further melting of the glacier. Kames are often associated with kettles.
Kames and kettles are just two of the many characteristic landforms created in the wake of a melting glacier.
2. Any interruption or break in the character of a slope.
A peak or projection from the top of a hill or mountain, or any rounded protrusion of land, especially a small but prominent or isolated hill with steep sides; a boulder or an area of resistant rock protruding from the side of a hill or mountain. The term is used primarily in the southern United States.
Also Gaussian process regression and Wiener–Kolmogorov prediction.
In geostatistics, an interpolation technique in which, for a given spatially dependent variable, a predicted value for an unmeasured location is derived by weighting the surrounding measured values based on the distance between them and to the unmeasured location, as well as the overall spatial arrangement of the measured points. Widely used in GIS applications, kriging is based on regionalized variable theory, which assumes that the spatial variation in the data being modeled is homogeneous across the surface.
Any piece of land connecting larger land areas that are otherwise separated by water, especially one over which living organisms, such as terrestrial animals and plants, are able to cross and thereby colonize previously inaccessible lands. Land bridges may be created by falling sea levels, tectonic activity, or post-glacial rebound. Compare isthmus.
The physical material present on the surface of the Earth, including categories such as vegetation (grasslands, shrubs, forests, etc.), bare ground, water, asphalt and artificial surfaces, and many others.
1. A broad or distinct area of land consisting of a collection of landforms which define a general geomorphologic form or setting, e.g. a mountain range, valley, plain, coast, etc. Landforms within a landscape are spatially associated but may vary in formation processes and age.
2. The visible features of an area of land, its landforms, and how they integrate with natural or man-made features. In the broadest sense, landscapes may include geophysical landforms such as hills and mountains; bodies of water such as rivers, lakes, and the sea; living elements of land cover such as vegetation; human elements such as buildings, structures, and various forms of land use; and transitory elements such as lighting and weather conditions. They reflect both physical origins and the cultural overlay of human presence in a living synthesis of people and place.
A measure of distance north or south of the Equator. One degree of latitude equals approximately 110 kilometers (68 mi). Lines of latitude, also called circles of latitude or parallels, are the imaginary lines that cross the surface of the Earth in an east-west direction (parallel to the Equator) and measure how far north or south of the Equator a place is located.
The side or slope of a physical feature (such as a hill or mountain) which faces downwind, i.e. away from the direction in which the wind is blowing, or which faces away from an advancing glacier or ice sheet. The lee side is often sheltered by the topography from exposure to the wind and any moisture it brings.
An elongated naturally occurring ridge or an artificially constructed wall or barrier which regulates water levels in areas prone to flooding. It is usually earthen and often parallel to the course of a river or a coastline.
The Earth's hard, outermost shell. It comprises the crust and the upper part of the mantle. It is divided into a mosaic of 16 major slabs or plates, which are known as lithospheric plates or tectonic plates.
A type of easily worked, highly fertile soil composed of clay, silt, and sand in an approximate ratio of 20:40:40. Loams generally heat rapidly, are well-aerated, and drain neither too quickly nor too slowly.
A measure of distance east or west of the Prime Meridian, a line drawn between the North and South Poles and passing through the Royal Observatory at Greenwich, England. Lines of longitude, also called meridians, are the imaginary lines that cross the surface of the Earth in a north-south direction (parallel to the Prime Meridian) and measure how far east or west of the Prime Meridian a place is located.
Any area of land that is lower in elevation relative to another area. The term is often used as a conditional descriptor to distinguish related habitats or ecosystems, especially freshwater riparian areas, on the basis of elevation above sea level. Lowland areas are usually relatively flat and characterized by slow-flowing waterways and alluvial plains. Contrast upland.
A local deviation from the predicted value of the Earth's magnetic field, due either to the presence of rocks formed in past geological eras which have preserved internal magnetizations that differ from modern magnetic alignments, or to local abundances or deficiencies of ferromagnetic minerals.
The angle on the horizontal plane between magnetic north and true north. Because compass needles always point to magnetic north, and because the Magnetic North Pole and the Geographic North Pole are not in precisely the same location, the north direction indicated by a compass may be slightly different from the direction of geographic north, depending on the user's location on the Earth. The user can compensate for this discrepancy by adding the known declination angle for their location to the magnetic bearing reported by their compass, yielding the true bearing with respect to true north.
The angle made with the horizontal by the Earth's magnetic field lines. Locations in the Northern Hemisphere usually have positive values of inclination, indicating that the magnetic field is angled downward, into the Earth; the angle increases as one approaches the North Magnetic Pole, where the field lines point vertically downward, perpendicular to the horizontal. Locations in the Southern Hemisphere usually have negative inclination, indicating that the field lines are angled upward, away from the Earth, with the maximum angle located at the South Magnetic Pole. Dip angle is in principle the angle made by the needle of a vertically held compass, though in practice ordinary compass needles may be deliberately weighted against dip, or may be unable to move freely in the correct plane. Magnetic dip can be measured more reliably with a dip circle.
A term used to denote a contiguouslandmass or political territory relative to its politically associated but geographically remote outlying territories. It is variously used to refer to the continental (i.e. non-insular) part of a polity relative to its exclaves or oceanic islands; or to the largest or most politically, economically, and/or demographically significant island within an island nation. For example, continental Europe is often considered "the mainland" relative to the British Isles, while the island of Great Britain is considered "the mainland" relative to Northern Ireland and the many smaller islands that constitute the United Kingdom.
A deep, closed valley (usually drained by a single wadi) surrounded by steep walls of resistant rock and superficially resembling a crater. The term is used primarily in the deserts of Israel and Egypt.
Smooth and rounded in appearance, used of various landforms of different sizes from individual rocks to entire landscapes.
The layer of the Earth's interior between the crust and the core, consisting of ultrabasic rock which is predominantly solid under the immense pressure of overlying rock but behaves as a viscous fluid over geological time scales or if this pressure is relieved (as with magma penetrating the crust). The mantle is about 2,900 kilometers (1,800 mi) thick, making up 84% of the Earth's volume and 67% of its mass. The uppermost sub-layer is known as the asthenosphere; the lithosphere is composed of the topmost 65–70 kilometres (40–43 mi) of the mantle and the crust.
A picture of a place drawn at an established scale on a two-dimensional plane surface, often depicting natural and manmade features on or under the surface of the Earth or other planetary body, typically with the features positioned as accurately as possible relative to a coordinate reference system; more generally, any graphical representation of locative information about the relative positions of particular features within a space or place.
A graphical key identifying the relationships between the individual maps of a map series, their coverage areas, and/or their production status or availability. Index maps enable users to find a map or set of maps covering a particular region of interest by overlaying a grid or a set of rectangles on a map of a larger geographical area. Each grid unit or rectangle is labeled with a name or number corresponding to a specific map sheet which depicts the indicated area in greater detail.
A systematic transformation of the latitudes and longitudes of locations from the surface of a three-dimensional shape, such as a sphere or an ellipsoid, into locations on a two-dimensional plane. Maps of locations on the Earth require map projections to represent features in a convenient format that is easy to view and interpret, though all map projections necessarily distort the true properties of the Earth's surface to some degree.
A group of topographic or thematic map sheets usually having the same scale and cartographic specifications and collectively identified by the publisher or producing agency as belonging to the same group.
A boundary, frontier, or borderland, as opposed to an interior heartland. In medieval Europe, a march was the land surrounding a border between realms, or a neutral buffer zone under the joint control of two or more realms with conflicting laws or territorial claims.
Land that is of low agricultural value because any crops produced from it would be worth the same or less than the costs paid to produce them, either because the rights or improvements required to cultivate it are very expensive, or the market prices for the crops are very low, or for any other reason. A change in economic conditions may allow formerly marginal lands to become profitable again.
1. Of, relating to, found in, or produced by the sea or ocean.
2. Of or relating to shipping or navigation, particularly by watercraft.
A climate strongly influenced by an oceanic environment, typically found on islands and the windward shores of continents. It is characterized by small daily and yearly temperature variation and high relative humidity.
The tendency of a firm or industry to be located close to wherever demand for the commodities it produces is strongest.
1. Any section of the Earth's crust which is demarcated by faults or flexures and tends to retain its internal structure while being displaced as a whole.
2. A single large mountain mass or compact group of connected mountains forming an independent portion of a mountain range.
In Switzerland and the Central Alps, a large shelf or ledge, intermediate between high alpine meadows and valley floors, where cattle are allowed to rest briefly during their annual movements between summer and winter pasture.
One of a series of regular sinuous curves, bends, loops, turns, or windings in the main channel of a river, stream, or other watercourse. Meanders are produced by the repetitive upstream erosion and downstream deposition of sediments along the banks of a watercourse as the water flows back and forth across the axis of a valley or floodplain.
The process by which the strip of land separating the two closest parts of a meandering river or stream channel is breached by the river's flow, forming a new, shorter channel that effectively "shortcuts" the loop of the meander and causes it to be gradually abandoned until it is completely isolated from the main flow. The river's course suddenly becomes much straighter, and the abandoned meander often forms a slackwater or an oxbow lake, or becomes loaded with sediment and dries up entirely, leaving visible traces of the former channel.
A meander cutoff occurs when a river erodes through the neck of a pronounced meander, creating a "shortcut" that isolates the meander loop from the river's main channel.
The narrow strip of land separating the river on each side of a well-developed meander. If this strip is completely eroded away, a cutoff occurs. See also neck.
A branch of human geography that studies the geographical aspects of health and the provision of healthcare, examining the spatial distribution of human diseases, mortality, morbidity, and the environmental factors conducive to human health and illness.
Also equatorial cylindrical orthomorphic map projection.
A conformalcylindricalmap projection in which the equator is represented by a straight line true to scale and meridians are represented by parallel straight lines perpendicular to the equator and uniformly spaced according to the distances between them at the equator. Lines of latitude are also represented by a system of straight lines which are perpendicular to all of the meridians and therefore parallel to the equator, though their spacing is not uniform but rather increases with increasing distance from the equator in order to conform with the expanding scale resulting from the parallel representations of the meridians. The standard Mercator projection has long been popular in navigation because it represents north as up and south as down everywhere in the world while preserving local directions and shapes, though it also greatly inflates the size of objects near the geographic poles.
A type of surveying in which boundaries are established with respect to ground features present at the time of the survey, which may include natural features and may or may not remain unchanged over time, e.g. a metes and bounds survey.
A line of longitude, i.e. any imaginary line connecting points of equal longitude and running perpendicular to all lines of latitude, intersecting them at right angles. Unlike lines of latitude, meridians are all the same length, but are not parallel to each other, instead converging at the geographic poles. Each meridian is half of a great circle drawn on the Earth's surface; the other half, connecting all of the meridian's antipodes, is termed an antimeridian. Meridians are numbered according to their longitudinal measure in angular degrees (further subdivided into minutes and seconds) up to 180 degrees east or west of an arbitrarily designated zero or prime meridian, by convention the International Reference Meridian.
A large city or conurbation which is considered a significant economic, political, or cultural center for a country or geographic region and/or an important hub for regional or international connections and communications.
A region consisting of one or more densely populated urban cores (often a metropolis) and its less populous surrounding territories, including satellite cities, towns, and intervening rural areas, all of which are socioeconomically tied to the core as typically measured by commuting patterns. A metropolitan area usually comprises multiple neighborhoods, jurisdictions, and municipalities, with its inhabitants sharing industry, housing, and many other forms of infrastructure.
A long, massive, man-made stone or earthen structure used as a pier or breakwater, or as a causeway between places separated by water, but designed to prevent the free movement of water underneath it (unlike a true pier).
The rocks and soil carried and deposited by a glacier. A terminal moraine, either a ridge or low hill running perpendicular to the direction of ice movement, is often visible near the end of a retreating glacier, indicating the glacier's maximum advance.
A large landform that rises prominently above the surrounding land in a limited area, usually in the form of a rocky peak with great vertical relief; a mountain is generally considered steeper than a hill. Mountains are formed by volcanic or tectonic forces and erode slowly through the actions of rivers, glaciers, and weathering. Most exist within extensive mountain ranges.
A series of neighboring mountains or hills, often closely arranged in a line and connected by high ground. Individual mountains within the same mountain range are usually the result of the same orogeny, and often (though not always) share a common form, alignment, and geology.
The ability to use more than one language when speaking or writing. This term often refers to the presence of more than two populations of significant size within a single political unit, each group speaking a different language as their primary language.
A type of general-purpose urbanadministrative subdivision having corporate status and powers of self-government or jurisdiction as granted by national and/or state laws to which it is subordinate. Municipalities are often included within but usually distinguished from larger administrative divisions such as counties, though the nature of their territorial boundaries and political jurisdictions can vary considerably in different parts of the world.
A governmental agency which manages, produces, and publishes topographic maps, geographic data, and sometimes cadastral information that is specific to an individual nation or political territory, such as the United Kingdom's Ordnance Survey.
A type of protected area created and managed as a public park by a national governmental authority for conservation purposes. Though individual governments designate national parks differently, they usually share the common goal of preserving natural or semi-natural landscapes (often wilderness) for posterity and as symbols of national pride.
A combination of a human settlement and an area of cultivated vegetation in an otherwise desolate desert or semi-desert environment, made fertile when sources of fresh water, such as underground aquifers, irrigate the surface naturally or via man-made wells.
The approximate geometric shape of the Earth: a three-dimensional ellipsoid that is nearly but not exactly a true sphere, being instead slightly flattened at the poles and slightly elongated at the equator.
The scientific study of the Earth's oceans and all processes and phenomena relating to them, including their formation and evolution over time; their physical and chemical properties and how these vary within the ocean and across its boundaries; their interactions with landmasses along coasts; the bathymetry and geology of the sea floor; currents, waves, and geophysical fluid dynamics; marine life and ecosystems; and how humans affect and are affected by oceans. The interdisciplinary field draws from and involves a diverse range of other sciences, including physics, biology, geology, hydrology, meteorology, and climatology, among others.
One of a series of regularly spaced bands of alternating height and color visible on the surface of some glaciers, resulting from seasonal patterns of alimentation and ablation. Because ice flows faster near the center of the glacier, where there is less friction with the surrounding glacial bed, ogives are usually shaped into conspicuous arcs that point towards the terminus of the glacier.
Any vertical datum used by the British Ordnance Survey as the basis for reporting elevations on maps. In modern Great Britain, the standard ordnance datum is the ODN, defined as the mean sea level calculated from hourly observations of the tidal gauge at Newlyn, Cornwall, between 1915 and 1921. All heights shown on British maps are measured from this benchmark.
The position of or the act of positioning a person or object with respect to the directional points of a compass, especially the placement of a map or surveying instrument in the field so that a north–south line on the map or instrument lies parallel to a north–south line on the ground. Determining one's orientation at a given time is the chief aim of orienteering, and is generally of critical importance in navigation.
An aerial photograph or satellite image that has been geometrically corrected or orthorectified such that the scale is uniform across all parts of the image, allowing the image to align with a particular map projection. In an uncorrected aerial photo, distances on the ground may be distorted by topographic relief, camera tilt, or the curvature of the Earth; techniques of digital image processing can compensate for these distortions, often by combining multiple images captured from slightly different perspectives into a single composite image. Orthophotos can be used to measure true distances because they accurately depict the relative sizes and positions of features on the Earth's surface.
Any visible exposure of bedrock or ancient superficial deposits on the surface of the Earth; or more generally, any bare, rocky surface that is topographically distinct from the surrounding terrain. Outcrops occur frequently in places where the rate of erosion exceeds the rate of weathering, such as on steep hillsides and mountains, river banks, and coastlines.
1. Alluvial sediment, usually consisting of fine sand, silt, and clay, that has been deposited on the floodplain of a river or stream by flood waters that have broken through or overtopped the river's banks.
2. The stage when a river or stream overflows the banks of its normal channel and spreads on to a floodplain, depositing such sediment.
An elliptical dome-like permafrost mound containing alternating layers of ice lenses and peat or mineral soil, commonly 3–10 metres (10–33 ft) high and 2–25 metres (7–82 ft) long, and occurring frequently in bogs in the Arctic and subarctic zones of discontinuous permafrost.
Any shallow, generally rounded basin or hollow, which may seasonally capture and hold water from rainfall or snowmelt, especially one occurring in an arid or semi-arid region; more specifically, the flat central part of such a depression, which may be temporarily or seasonally flooded.
A rounded or circular depression eroded into flat or gently sloping cohesive rock, typically shallow and ranging in diameter from a few centimeters to several meters, that is capable of collecting and holding rainwater and snowmelt. The term is sometimes used interchangeably with pothole, though the latter may also refer to distinct geological features.
An instrument that enables the mechanical copying of a map or technical drawing on a selectable scale, such that the movement of one pen, in tracing an image, produces identical movements in a second pen, resulting in a duplicate image that is the same size, enlarged, or miniaturized with respect to the original. Pantographs typically consist of hinged rods arranged in the shape of a parallelogram which rotate about a fixed point.
1. (geometry) Extending in the same direction, equidistant at all points, and never converging or diverging; having the same orientation, nature, tendency, or course; corresponding or similar.
A glacier with low rates of both alimentation and ablation because it receives only light snowfall and undergoes little melting throughout the year. Such glaciers move very slowly and transport relatively small amounts of ice and debris. Contrast active glacier.
Any land used for grazing by livestock, often a natural grassland supporting native grasses and forbs with little or no active management by humans, as opposed to a meadow, where the vegetation is mown for hay or silage.
An eroded, often bare rock platform, cut into the local bedrock, usually slightly concave and triangular in shape and extending over a considerable area at the foot of an abrupt mountain slope or face, the lower edge sloping gently away. Pediments form basal slopes of transport for weathered material derived from the steeper slope above, and are characteristic of arid and semi-arid lands.
A historical manuscript listing the ports, safe anchorages, and coastal landmarks that a maritime vessel could expect to encounter along a shore or coastline, arranged in order according to a particular direction of travel and including the intervening distances between them. See also itinerarium.
Also euphotic zone, epipelagic zone, and sunlight zone.
The uppermost layer of a body of water (e.g. a lake or ocean), defined by the maximum depth to which sunlight can penetrate the water column. The photic zone usually supports large populations of photosynthetic organisms and the majority of the aquatic life inhabiting the body as a whole.
1. The science and technology of obtaining reliable information about physical objects and environments through the process of recording, measuring, and interpreting photographic images (usually aerial or orbital ones) and patterns of electromagnetic radiant imagery and other phenomena.
2. The science of extracting three-dimensional measurements from two-dimensional data, such as images.
A periglacial landform consisting of a relatively large conical mound of soil-covered ice, commonly 30–50 metres (100–160 ft) high and up to 1,000 metres (0.6 mi) in diameter, and that grows and persists in part as a result of hydrostatic pressure within and below the permafrost of Arctic and subarctic regions.
The measure of approval or satisfaction accorded by an individual to a location in his or her action space; the value or usefulness of a particular place as perceived by a particular person. Dissatisfaction with place utility may result in migration.
1. (mineral deposit) An accumulation of valuable minerals, particularly gold, formed by gravity separation from a source rock during natural sedimentary processes. The minerals, weathered from rocks or veins, are washed out by streams and mixed with alluvial deposits of sand or gravel, from which they can then be extracted by placer mining.
2. (reef) A flat, shallow sandbank or reef submerged beneath the ocean surface, often with a sandy bottom suitable as an anchorage for seagoing vessels.
A small drawing board mounted on a tripod used in surveying, site mapping, and related disciplines to provide a solid and level surface upon which to make drawings, charts, and maps while in the field.
A map which uses a two-dimensional coordinate system, i.e. in which each point is represented by only two coordinates (x, y), as if all of the depicted features existed within a single, flat plane. These maps usually exclude information about vertical position and therefore do not show topographic relief and represent only horizontal distances.
A cadastral map, drawn to scale, showing the legal boundaries and divisions of a surveyed tract of land, particularly of the type used to divide real property for sale and settlement in the Public Land Survey System of the United States.
An exceptionally flat, arid basin that is the dry bed of an evaporated lake; or the shallow, usually saline lake itself which periodically forms when the basin is temporarily covered with water, e.g. after substantial rainfall. See also salt pan.
An erosional phenomenon whereby a glacier gradually scours and displaces pieces of rock from the bedrock beneath it and transports them along with the glacial flow of ice and debris. As the glacier moves down a valley, friction causes the basal ice to melt and infiltrate joints and cracks in the bedrock; repeated freezing and thawing widens and deepens these cracks, eventually loosening the rock and causing large blocks and boulders to be carried along by the overlying ice. These boulders are often deposited hundreds of kilometers from their source, becoming erratics. The term is also sometimes used to describe the similar process of quarrying, which occurs on a smaller scale in fast-moving rivers and streams.
A vertical reference line created by suspending a weight, known as a plumb bob or plummet, from a string above the Earth's surface and allowing it to hang freely in the direction of the pull of gravity. A precursor to the spirit level, plumb lines are used to establish a vertical datum in a wide range of applications, particularly in surveying to determine the nadir of a point in space, and often in combination with an instrument in order to set the instrument precisely over a fixed survey marker.
A deep depression at the base of a waterfall into which the water drops with great force, plucking and abrading the rock beneath and behind the falls and creating an often nearly circular concavity which may remain filled with water long after the waterfall itself dries up.
Either of the two very large regions near the Earth's geographical poles that are seasonally or persistently covered in ice, which occurs because high-latitude regions receive less direct solar radiation than other regions and therefore experience much lower surface temperatures. The Earth's polar ice may cover both land and sea, and varies in size seasonally and with long-term climate change. They typically cover a much larger area than true ice caps and are more correctly termed ice sheets.
Either of the two high-latitude regions surrounding the Earth's geographical poles (the North and South Poles), which are characterized by frigid climates and extensive polar ice caps. The polar region of the Northern Hemisphere is often simply called the Arctic and that of the Southern Hemisphere is called the Antarctic.
A low-lying tract of land enclosed by dikes, forming an artificial hydrological entity by creating land from a naturally inundated area, e.g. by reclaiming land from a lake or sea, or by building barriers around a floodplain or marsh and then draining it. All polders are eventually below the surrounding water table some or all of the time, making them especially prone to flooding, and they often require continuous draining.
1. An extreme geographical point, especially one of a pair.
A location that, with respect to a given geographical criterion, is the most difficult to reach according to that criterion, e.g. the geographical location that is the most distant from the nearest point meeting that criterion. The term most commonly refers to the so-called continental or oceanic poles of inaccessibility, i.e. the point on a given continental landmass that is the furthest distance from a coastline, and the point in the ocean that is the furthest distance from land, respectively.
The study of both the spatially uneven outcomes of political processes and the ways in which political processes are themselves affected by spatial structures. A sub-discipline of human geography, its primary concerns can be summarized as the relationships between people, state, and territory.
A very large plain found in karstic regions, enclosed within a depression, usually elliptical, with a flat floor either of bare limestone or covered by alluvium, and generally surrounded by steep limestone walls; or more broadly any enclosed or nearly enclosed valley. The term is used primarily in the Slavic-speaking world.
An area of unfrozen seawater surrounded by an otherwise contiguous area of pack ice or fast ice. Polynyas are often formed along polar coastlines through the action of katabatic winds, but may also form in the open ocean.
A collection of organisms of the same group or species which live in a particular geographical area. In the context of geography, it often refers to a collection of humans and is represented at the most basic level as the number of people in a given geographically or politically defined space, such as a city, town, region, country, or the entire world.
A branch of human geography that studies the ways in which spatial variations in the composition, distribution, migration, and growth of populations are related to the nature of places. This often involves factors such as where populations are found and how the size and composition of these populations is regulated by the demographic processes of fertility, mortality, and migration.
Any technology or mechanism used to determine the position of an object in space. Numerous methods for determining position have been practiced since ancient times, though modern positioning systems generally rely on electromagnetic and/or satellite-based technologies capable of providing coverage ranging from local or regional to global and accuracy ranging from tens of metres to sub-millimetre.
Also pot, swirlhole, churn hole, evorsion, rock mill, and eddy mill.
1. Any smooth, bowl-shaped or cylindrical hollow, generally deeper than it is wide, that is carved into the rocky bed of a watercourse such as a stream or river. Fluvial potholes are created by the grinding action of stones or coarse sediment kept in perpetual motion in the same spot by the turbulence of the current. The term is also used to refer to plunge pools beneath waterfalls, which are created by similar processes. See also kolk.
A type of temperate grassland ecosystem dominated by a characteristic composition of grasses, herbs, and shrubs, rather than by trees. The term is used primarily in North America, but similar ecosystems can be found across the world.
The natural extension of a shoreline into a body of water by the gradual accumulation of sediment over time, especially as a result of fluvialsedimentation processes, such as the protrusion of a river delta into the sea. This occurs when the volume of sediment carried by the river and deposited at its mouth exceeds the volume lost through subsidence, sea level rise, or coastal erosion.
Any clearly defined geographic space in which human occupation or the exploitation of resources is limited or forbidden through legal or other effective means because of the area's recognized natural, ecological, cultural, or historical value.
A type of Indian village constructed by some tribes in the southwestern United States. A large community dwelling, divided into many rooms, up to five stories high, and usually made of adobe. This is also a Spanish word for town or village.
A standard division of the Earth's surface area used in maps produced by the United States Geological Survey. Quadrangles are four-sided polygons of varying size, depending on the map series; for example, 7.5-minute quadrangles divide the mapped surface into quadrilaterals measuring 7.5 minutes (0.125 degrees) of latitude by 7.5 minutes of longitude, with each 7.5-minute map showing the topographical detail within one particular quadrilateral of this size. Because the boundaries of quadrangles are based on lines of latitude and longitude, the northern and southern limits of a quadrangle map are not straight lines, and the eastern and western limits are usually not parallel; the actual surface area covered by each map varies with the latitudes depicted.
The distance between the two rails of a railroad.
The track or trace of a railroad route, commonly raised slightly above the adjacent natural ground surface and constructed mostly of locally occurring, earthy materials (e.g. gravel and rock fragments).
Any forest characterized by abundant rainfall, dense layers of vegetation, and extremely high biodiversity. Rainforests are found in both tropical and temperate regions. The term jungle is sometimes used to refer to a tropical rainforest.
A sloping terrace on a mountainside or rock face. The term is used primarily in Scotland.
A representation of spatial data within a two-dimensional image that defines space as a rectangular array or grid of equally sized cells arranged in rows and columns, where each cell can be identified with location coordinates and is associated with attribute values containing a discrete amount of information from one or more layers or "bands". Raster models are useful for storing and presenting large amounts of complex multivariate data that vary continuously across space, as is commonly encountered in maps, aerial photographs, satellite imagery, and many other aspects of geographic information science. Raster data are contrasted with vector data, which instead store and represent geographic information in the form of points, lines, and polygons.
A fluvial slope landform of relatively steep sides, sometimes with an intermittent stream flowing along the downslope channel. Ravines are typically narrower and shallower than canyons, larger than gullies, and smaller than valleys.
1. Any land area that is artificially created from earthy fill material that has been intentionally placed and shaped so as to approximate natural contours, especially as part of land reclamation efforts such as those designed to bury tailings following the cessation of mining operations.
2. An area of land, commonly submerged underwater in its natural state, that has been protected by artificial structures such as dikes and drained for agricultural or other purposes (e.g. a polder).
A submerged ridge-like or mound-like structure built by sedentary calcareous organisms, especially corals, in shallow marine waters, and consisting primarily of their skeletal remains, though often still supporting living colonies as well. Reefs may also be partially composed of rocks, sand, gravel, or seashells. They are locally prominent above surrounding sediments deposited on the sea floor, rising to or nearly to the water's surface.
An area having some characteristic or characteristics that distinguish it from other areas; a territory that is of interest to people, for which one or more distinctive traits (e.g. climate, economy, history, etc.) define its identity.
1. The feeling or expression of a common sense of identity, purpose, or group consciousness associated with a particular geographical region, e.g. the Southern United States, Scandinavia, or Lower Egypt, often combined with the creation of institutions that accommodate that particular identity and shape public action.
2. A movement to decentralize central government, placing administrative responsibility instead at a level intermediate between that of the state and that of smaller local or municipal units.
3. In architecture, an approach that strives to counter placelessness and lack of identity by incorporating elements of the building's geographical context in its design.
(of a particular location) Isolated or inaccessible, either by being physically very distant from another location or by lacking connectivity to transportation or communication networks which would otherwise make exchange between locations convenient.
The gathering of information about an object or place from a remote location (i.e. without making physical on-site observations), most commonly by the use of satellite- or aircraft-based electromagnetic sensor technologies.
The fraction expressing the ratio between the distance measured between two points on a map and the corresponding actual distance measured between those points in the real world, used to indicate the map's scale. The fraction's numerator is typically 1 (indicating one of some specified unit of length, e.g. inches or centimetres) and the denominator is the number of the same unit in the real world which this length represents on the map. For example, a representative fraction of 1⁄1,000,000, often written as 1:1,000,000 or 1:1 mn, means that one inch (or one centimetre) on the map itself is equivalent to one million inches (or centimetres) in the real world. One statute mile is equal to 63,360 inches, so 1,000,000 inches is approximately 16 miles.
A line drawn on the surface of a sphere (or on an idealized representation of the Earth) which crosses all meridians of longitude at the same angle, and which therefore has constant bearing relative to true or magnetic north.
A rhumb line or loxodrome spirals toward the north pole of a sphere, crossing all lines of longitude at the same angle.
The build-up of residential and economic communities along the main routes of communication and transportation radiating from a city or other developed area, because of the advantages of accessibility, relatively inexpensive land, and trade from passers-by.
An elongated raised landform which forms a continuous elevated crest for some distance, such as a chain of hills or mountains. The line formed by the highest points, with only lower terrain immediately to either side, is called the ridgeline.
An area of land enclosed within the bend of a river, especially where the bend is extended or pronounced (e.g. a meander) and the only road access is along the isthmus. The term is used primarily in Australia.
1. A way or course taken in getting from one place to another; an established or selected course of travel or action; a line of travel or means of access, especially when marked by a path, track, road, or rail.
2. A circuit traveled in delivering, selling, or collecting goods, e.g. by a mail carrier.
The determination of a viable route or line of travel between two places, especially in rugged or unexplored areas such as mountainous terrain or in conditions of poor visibility, and especially when done without the benefits of prior knowledge of the area, maps, or other technology that might aid orienteering, instead relying entirely on recognition of natural features and landmarks and quick estimations of distance, scale, ease, and safety.
An adjective describing any geographic area located outside areas of significant human population such as towns and cities; all population, housing, and territory not included within an urban area is often said to be rural. Rural areas are typified by low population densities, very small settlements, and expansive areas of agricultural land or wilderness.
For a given pair of mountain summits, the region surrounding the elevational low point or col on the ridge connecting the two summits; mathematically, it is the critical point that is simultaneously a relative minimum in one axial direction (e.g. between the peaks) and a relative maximum in the perpendicular direction. Assuming it is navigable, a saddle can be thought of as the area surrounding the highest point on the lowest route which one could use to pass between the two summits.
The saddle is the highest point of the pass between the two mountains.
A natural coastalmarsh ecosystem in the upper intertidal zone, between land and open seawater or brackish water, that is regularly flooded by the tide at high water. Salt marshes support dense stands of terrestrial salt-tolerant plants, especially grasses and low shrubs, which trap and bind sediments from the ocean and help protect the nearby shoreline from coastal erosion.
A large, flat expanse of land naturally covered with salt and/or other minerals, usually to the exclusion of virtually all vegetation. Salt pans are common in deserts, where they form by the precipitation of dissolved mineral solids as a large body of water evaporates. See also playa.
Any naturally occurring water, especially the water from a sea or ocean, characterized by high concentrations (between 3 and 5% by volume) of dissolved salts, primarily sodium and chloride ions, relative to fresh water or brackish water. Salt water in the Earth's oceans has an average salinity of about 3.5%; it is both denser and freezes at a lower temperature than fresh water.
A method of navigation or an autonomous geospatial positioning system that relies on artificial satellites in orbit around the Earth to transmit time signals at radio frequencies along a line of sight to electronic receivers on the surface, which can then use this information to determine their location, direction, and the current local time to high precision. Satnav systems operate independently of telephonic or internet connectivity, though simultaneous use of these technologies can enhance the accuracy and usefulness of the positioning information generated.
A mixed woodland-grassland ecosystem characterized by scattered trees and bushes that are sufficiently widely spaced that the canopy does not close, permitting enough sunlight to reach the ground to support an unbroken herbaceous layer of primarily xerophytic grasses. The term is used especially to refer to the vast, hot, arid grasslands covering parts of equatorial Africa, South America, and northern Australia, but is also sometimes applied more broadly.
The average level of the surface of one or more of Earth's oceans from which heights such as elevation and altitude are commonly measured. Often called mean sea level (MSL), it is a type of standardized geodeticvertical datum that is used in numerous applications, including surveying, cartography, and navigation. Mean sea level is commonly defined as the midpoint between the mean low and mean high tides at a particular location.
In human geography, the locations within an area where an individual or group searches for the resources necessary to meet their specific needs (e.g. for housing or employment), based on information from their current awareness space.
A seasonally occupied dwelling that is not the primary residence of the owner. Such residences are usually found in areas with substantial opportunities for recreation or tourist activity.
The set of eight intermediate directions used in cartography and navigation, each of which is located halfway between a pair of intercardinal directions: north-northeast (NNE), east-northeast (ENE), east-southeast (ESE), south-southeast (SSE), south-southwest (SSW), west-southwest (WSW), west-northwest (WNW), and north-northwest (NNW). They may or may not be explicitly labeled on a compass rose.
That portion of a region's economy devoted to the processing of basic materials extracted by the primary sector.
The principle on which political claims to territory in the polar regions have historically been made, such that the territories are divided into arbitrary wedge-shaped sectors, each one having an apex at the geographic pole and including outer areas of both land and sea extending to a particular latitude. Because of the limited accessibility and generally low material value of both the Arctic and Antarctic, the sector principle has emerged as a means of formally sharing responsibility for these regions between the world's sovereign states.
A large block or pillar of glacial ice formed by the intersection of numerous crevasses where the glacier fragments as it reaches a steep slope. Seracs are usually found in icefalls, often in large numbers, in mountainous terrain.
The phenomenon by which a large, well-served urban center affects the transport services of a nearby smaller town or city, often by drawing producers and consumers away from the smaller settlement and toward the larger one, causing the smaller settlement to be relatively ill-provided with direct services.
A rock formation created by the passage of a glacier over underlying bedrock, which often results in asymmetrical erosional forms created by abrasion on the upstream side of the rock and plucking on the downstream side.
The brief period of time during which a body of water susceptible to tides is completely unstressed because the tidal stream is almost still, i.e. there is no movement in either direction in the tidal current, usually the period immediately before and after the high and low water marks, prior to the tide reversing direction.
The line-of-sight distance along the relative direction between two points, especially two points which are not at the same elevation relative to a specific datum. If the two points are at the same elevation, the slant range equals the horizontal distance.
1. In the southeastern United States, a low-lying swampy or boggy area, overgrown with shrubs and cane grasses and favorable for the growth of the slash pine and related trees.
Cross-section of a meandering river: uneven currents result in asymmetrical channels with a gently sloping depositional bank, known as a slip-off slope, on the inside of each bend and a steep erosional bank, known as a cut bank, on the opposite side.
The upward or downward inclination of a natural or artificial surface (e.g. a hillside or a road), or the degree or nature of such an incline; a deviation from the perpendicular or horizontal direction (these directions generally being assigned with respect to the direction of the force of gravity). See also grade.
A residential settlement or neighborhood, usually in or near an urban area, characterized by densely packed and poorly built or dilapidated housing units such as shacks and a deterioration or lack of civic infrastructure such as reliable water, electricity, sanitation, law enforcement, and other basic services, and usually associated with extreme poverty and overpopulation.
A statistical unit of one or more counties that focus on one or more central cities larger than a specified size, or with a total population larger than a specified size. This is a reflection of urbanization.
The lowermost margin or extremity of a glacier, always either gradually advancing or retreating, sometimes partially hidden by morainic material, and commonly featuring a cave from which meltwater flows.
The lowest elevation at which snow remains throughout the year if the summer warmth does not completely melt the winter accumulation, e.g. on a high mountain. This elevation varies widely with latitude, local climate, directional aspect, and steepness of slope, such that the snowline may be very different on different mountains in the same range, on different faces of the same mountain, or on the same face in different years.
The degree to which a substance can be dissolved in another substance; in a geographical context, the characteristic of soil minerals that leads them to be carried away in solution by water. See also leaching.