Equator and Prime Meridian

Imagine a line wrapped around Earth halfway between the North and South Poles. That is the equator, at zero degrees latitude. Latitude lines run east-west, parallel to the equator, and tell us how far north or south a place lies.

The prime meridian runs from the North Pole to the South Pole through Greenwich, England. It marks zero degrees longitude. Longitude lines run north-south and tell us how far east or west a place lies. Together latitude and longitude can name a position.

The equator is a natural halfway circle. The choice of which longitude line to call zero was an agreement among people. Neither line is a wall you can see on the ground; they are map tools for directions and measurements.