The city hosting the historic Prime Meridian at Greenwich is London.
The Greenwich meridian is the reference line for zero degrees longitude. It passes through the Royal Observatory in Greenwich, a district in southeast London. From this line, longitude is measured eastward and westward around Earth, helping establish global maps, navigation, and timekeeping.
An international conference in Washington, D.C., in 1884 selected Greenwich as the world’s prime meridian. The choice reflected the widespread use of British nautical charts and the importance of the Royal Observatory in astronomy and navigation. Greenwich Mean Time later became a major international time standard.
Modern satellite-based geodesy places the precise zero-longitude line about 102 meters east of the historic observatory line. This difference results from changes in reference systems and the shape of Earth. The historic meridian remains a famous visitor landmark, while Coordinated Universal Time is now the principal global time standard.