A
geographic coordinate system is a
coordinate system that enables every location on Earth to be specified in three coordinates, using mainly a
spherical coordinate system.
The Earth is not a sphere, but an irregular shape approximating an ellipsoid; the challenge is to define a coordinate system that can accurately state each topographical point as an unambiguous tuple of numbers.[1]
A line passing to the rear of the Royal Observatory, Greenwich (near London in the UK) has been chosen as the international zero-longitude reference line, the Prime Meridian. Places to the east are in the eastern hemisphere, and places to the west are in the western hemisphere. The antipodal meridian of Greenwich is both 180°W and 180°E.
In 1884, the United States hosted the International Meridian Conference and twenty-five nations attended. Twenty-two of them agreed to adopt the location of Greenwich as the zero-reference line. San Domingo voted against the adoption of that motion, while France and Brazil abstained.[2] To date, there exist organizations around the world which continue using historical prime meridians before the acceptance of Greenwich and the ill-attended conference became common-place.[3]
