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A spherical coordinate system that enables every location on Earth to be specified in coordinates. Lines joining points of the same latitude are called parallels, which trace concentric circles on the surface of the Earth, parallel to the equator.
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Latitude phi (f) and Longitude lambda (?)Latitude (abbreviation: Lat., f, or phi) is the angle from a point on the Earths surface to the equatorial plane, measured from the center of the sphere. Lines joining points of the same latitude are called parallels, which trace concentric circles on the surface of the Earth, parallel to the equator. The north pole is 90° N; the south pole is 90° S. The 0° parallel of latitude is designated the equator, the fundamental plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres.
Longitude (abbreviation: Long., ?, or lambda) is the angle east or west of a reference meridian between the two geographical poles to another meridian that passes through an arbitrary point. All meridians are halves of great circles, and are not parallel. They converge at the north and south poles.
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.