# Geographic coordinate system

## System to specify locations on Earth / From Wikipedia, the free encyclopedia

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A **geographic coordinate system** (**GCS**) is a spherical or geodetic coordinate system for measuring and communicating positions directly on Earth as latitude and longitude.^{[1]} It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others. Although latitude and longitude form a coordinate tuple like a cartesian coordinate system, the geographic coordinate system is not cartesian because the measurements are angles and are not on a planar surface.^{[2]}

A full GCS specification, such as those listed in the EPSG and ISO 19111 standards, also includes a choice of geodetic datum (including an Earth ellipsoid), as different datums will yield different latitude and longitude values for the same location.^{[3]}