Greenwich meridian, imaginary line used to indicate 0° longitude that passes through Greenwich, a borough of London, and terminates at the North and South poles. An international conference held in Washington, D.C., in 1884 designated “the meridian passing through the centre of the transit instrument at the Observatory of Greenwich as the initial meridian for longitude.” The observatory (renamed the Royal Greenwich Observatory) was moved to Hailsham, East Sussex, during the 1950s, but the original site continues to serve as the location for 0° longitude.
Greenwich
By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their charts and maps. In October of that year, at the behest of U.S. President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., USA, for theInternational Meridian Conference. This conference selected the meridian passing through Greenwich as the official prime meridian due to its popularity. However, France abstained from the vote and French maps continued to use the Paris meridian for several decades. In the 18th century, London lexicographer, Malachy Postlethwayt published his African maps showing the 'Meridian of London' intersecting the Equator a few degrees west of the later meridian and Accra, Ghana.