What do longitude lines measure?

Longitude lines measure the east-west position of a point on the Earth's surface relative to the Prime Meridian, which is defined as 0 degrees longitude. These lines run vertically from the North Pole to the South Pole and help in identifying a specific location's position on a globe or map in relation to this reference point.

By knowing the longitude of a location, we can determine how far east or west it is from the Prime Meridian, which is crucial for navigation and understanding time zones. Each degree of longitude corresponds to a specific distance along the Earth's surface, which can vary slightly due to the curvature of the Earth, but the fundamental concept remains anchored to this measurement from the Prime Meridian.