Longitude

Geographers use a coordinate system to specify any location on the surface of the earth. One axis of this system consists of lines running North and South, called lines of longitude. These lines are sometimes called meridians.

Each line of longitude is a half-circle connecting the earth's North and South poles. The lines are identified by their angular distance from the Prime Meridian. For example, the line falling 90 degrees West of the Prime Meridian is known as the 90th meridian, or 90 degrees West longitude.

The other axis consists of lines circling the globe running East and West, called lines, or circles, of latitude.