The Geographical Longitude of position “L” is the arc measured on the Equator that is included between the Prime Meridian and the Meridian passing through “L”.
The longitude is defined as East (E), if the position is in the eastern hemisphere, or West (W) if the position is in the western hemisphere.
The longitude is measured in degrees, minutes and seconds, starting from 0 degrees at the Prime Meridian, going up to 180 degrees East (E) or 180 degrees West (W).
As with latitude, every degree has 60 minutes and every minute has 60 seconds.