Longitude

Longitude, measure of the distance, in angular degrees, of any point on the earth's surface east or west of the prime meridian, which is 0° longitude. The prime meridian is the imaginary great circle line, running from pole to pole, that runs through the city of Greenwich, England. Meridians of longitude and parallels of latitude form a grid that can be used to locate the position of any point on the earth's surface.

See also: Latitude; Prime meridian.