Longitude lines measure degrees west or east of which reference point?

Longitude lines measure degrees east or west of the Prime Meridian. The Prime Meridian is the designated zero degrees longitude line, which runs through Greenwich, England. It serves as the starting point for counting degrees of longitude. As you move to the east from the Prime Meridian, the degree measurements increase up to 180 degrees, while moving to the west decreases down to -180 degrees.

This reference point is essential for navigation and mapping, as it helps in determining a specific location on the globe. By understanding where the Prime Meridian lies, one can easily calculate the longitudinal position of any point on Earth.