The Western Hemisphere is the half of Earth which lies west of the prime meridian (which crosses Greenwich, London, United Kingdom) and east of the antimeridian. The other half is called the Eastern Hemisphere. In geopolitical terms, the context in which the term is most often used, the Encyclopedia Britannica defines it as "North and South America and the surrounding waters. Longitudes 20°W and 160°E are often considered its boundaries." It may be used in a cultural or geopolitical sense as a synonym for the "New World".
As an example of totum pro parte, the term Western Hemisphere is widely used by some, such as the United States government, to refer to the Americas.
The Western Hemisphere consists of the Americas, excluding some of the Aleutian Islands to the southwest of the Alaskan mainland; the westernmost portion of Europe, both mainland and islands; the westernmost portion of Africa, both mainland and islands; the extreme eastern tip of the Siberian mainland and islands (Russian Asia); numerous territories in Oceania; and a large portion of Antarctica.
The center of the Western Hemisphere is located in the Pacific Ocean at the intersection of the 90th meridian west and the Equator, among the Galápagos Islands. The nearest land is Genovesa Island at.
The highest mountain in the Western Hemisphere is Aconcagua in the Andes of Argentina at 6,960.8 metres (22,837 ft).
The tallest human-occupiable building or tower in the Western Hemisphere is the CN Tower, which is located in Toronto, Canada at.
In an attempt to define the Western Hemisphere as the parts of the world which are not part of the Old World, there also exist projections which use the 20th meridian west and the diametrically opposed 160th meridian east to define the hemisphere. This projection excludes the European and African mainlands and a small portion of northeast Greenland, but includes more of eastern Russia and Oceania.
Below is a list of the sovereign states in both the Western and Eastern hemispheres on the IERS Reference Meridian, in order from north to south:
Below is a list of additional sovereign states which are in both the Western and Eastern hemispheres along the 180th meridian, in order from north to south. (France is not listed below due to its inclusion above, though the meridian does pass Wallis and Futuna.) With the exception of the United States (due to Wake Island, Guam and the Northern Mariana Islands), all of them are located on just one side of the International Date Line, which curves around them.
One sovereign state has territory in both hemispheres, but neither the prime meridian nor the 180th meridian passes through its territory:
The following countries and territories lie outside the Americas yet are entirely, mostly or partially within the Western Hemisphere: