Western Hemisphere

Definition and boundaries

In cartography the Western Hemisphere is most often defined as all points with longitudes between 0° (the Prime Meridian) and 180° west. Some usages simply mean the half of the globe west of the Prime Meridian. Because meridians converge at the poles, the boundary is a great circle that runs from the North Pole to the South Pole. Different contexts—political, cultural or astronomical—may shift the practical meaning.

Geographic composition

• The Americas: virtually the whole of North and South America and their offshore islands.
• Adjacent ocean areas: much of the Pacific and the entirety of the Atlantic basin bordering the Americas.
• Fringes of other continents: small parts of western Europe and western Africa fall within the western meridian range depending on the definition used.

For maps and atlases consult general references or a globe to see the meridians; introductory materials often point to the North Pole, through Greenwich, to the South Pole when explaining the split. See a basic note on Earth orientation at this overview.

History and uses

The division into eastern and western hemispheres emerged with improved global navigation and the adoption of standardized meridians in the 18th and 19th centuries. It has been used in navigation, timekeeping, geopolitics and education to describe location, climate patterns and international relations. Historical references to the "New World" are tied to the Western Hemisphere in a cultural sense rather than strictly geometric bounds; for context consult a discussion of transatlantic exploration here.

Notable distinctions and practical points

Unlike the equator, which divides the planet into Northern and Southern Hemispheres with clear climatic and astronomical consequences, the eastern/western split is arbitrary and depends on the chosen meridian. Political groupings, economic regions and cultural areas rarely align exactly with hemispheric lines. For examples of how hemispheric concepts are applied in law, climate studies and mapping, see resources at link, link and link.

Summary: The Western Hemisphere is a human-defined half of Earth useful for orientation and discussion. Its precise limits follow meridians but its significance varies with context.