Maping Longitude and Latitude

Longitude lines have a Meridian which it passes through 0 degrees longitude. The lines of longitude run North To South when you are looking at a map. They measure the distance east to west of the Prime Meridian. The Prime Meridian is furthest from the equator and they meet at the poles. All the lines are equal length from each other. They are each equal length east, to west, not north to south.
Longitude is measured by imaginary lines running parallel to the equator and used to measure the distance in degrees north or south of the equator. That is the definition of Longitude.