What longitude is represented by the prime meridian?

The prime meridian is defined as 0° longitude and serves as the starting point for measuring longitude both east and west around the Earth. It runs through Greenwich, London, and by convention, all other longitudes are expressed in degrees relative to this line.

When you measure east from the prime meridian, the longitudes increase up to 180°E, and when you measure west, they increase up to 180°W. Because the prime meridian itself is the reference line, it is designated as 0°. This understanding is fundamental in geography as it assists in mapping and navigation, allowing for a coordinated system of geographic reference that is universally recognized.