Which line defines the starting point for measuring longitude?

The Prime Meridian serves as the foundational reference line for measuring longitude. Situated at 0 degrees longitude, it runs through Greenwich, England, and acts as the baseline from which all other longitudes are determined. Longitude lines are measured in degrees east or west of the Prime Meridian, reaching up to 180 degrees in both directions.

This reference is crucial for navigation and geography, as it helps to establish a standardized system for locating places on the Earth's surface. While the Equator is important for measuring latitude and divides the Earth into the Northern and Southern Hemispheres, it does not play a role in longitude measurement. The International Date Line primarily serves as the demarcation for calendar days and does not serve as a starting point for measuring longitude either. The North Pole, while significant in terms of geographic coordination, does not function as a longitudinal reference point. Instead, it represents a location on the Earth rather than a line of reference for measurement.