The Western Hemisphere is the half of Earth that 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. Politically, the term Western Hemisphere is often used as a metonymy for the Americas, even though geographically the hemisphere also includes parts of other continents.
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 Russian mainland and islands (North 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 m (22,837 ft).
The tallest freestanding structure in the Western Hemisphere is the CN Tower in Toronto at 553.3 m (1,815 ft) and the tallest building in the Western Hemisphere is One World Trade Center in New York City at 541.3 m (1,776 ft).
In an attempt to match the Western Hemisphere more closely with the Americas, some sources use the 20th meridian west and the diametrically opposed 160th meridian east to define the hemisphere. This definition excludes all of the European and African mainlands, but still includes some islands associated with these continents, more of eastern Russia and Oceania, and part of Antarctica. It includes all islands of Alaska, but excludes a small portion of northeast Greenland. There is no hemisphere that includes all of the Americas while excluding all land outside of it, regardless of the meridians or points chosen to define it.
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.
The following countries and territories lie outside the Americas yet are entirely, mostly, or partially within the Western Hemisphere: