a method to measure the earth representing angles of a line extending from the center of the earth to the earth's surface; with a line extending from the north to the south pole and passing through Greenwich, England, as 0°, angles are measured in degrees east or west until 180° is obtained at the opposite side of the earth from 0° longitude —note lines of longitude are often called meridians —see latitudeThis definition last updated 07/13/2008