Longitude

Angular distance east or west of the reference meridian, expressed from 0 degrees to 180 degrees.

Longitude identifies a meridian on a chosen geodetic reference system and is written with E or W, commonly in degrees and decimal minutes or decimal degrees. The internationally adopted reference meridian passes through Greenwich, and longitude combined with latitude identifies a position.

The east-west distance represented by one minute of longitude decreases from its maximum at the Equator to zero at the poles. Hemisphere, datum and coordinate format must be retained because omitting E or W or confusing minutes with decimal degrees can create a large position error.