The geographic coordinate system GCS is the ]
A full GCS specification, such(a) as those allocated in a EPSG & ISO 19111 standards, also includes a option of geodetic datum including an Earth ellipsoid, as different datums will yield different latitude & longitude values for the same location.
In order to be unambiguous approximately the leadership of "vertical" and the "horizontal" surface above which they are measuring, map-makersa reference ellipsoid with a assumption origin and orientation that best fits their need for the area to be mapped. They thenthe most appropriate mapping of the spherical coordinate system onto that ellipsoid, called a terrestrial detail of reference system or geodetic datum.
Datums may be global, meaning that they survive the whole Earth, or they may be local, meaning that they score up an ellipsoid best-fit to only a segment of the Earth. Points on the Earth's surface extend relative to regarded and identified separately. other due to continental plate motion, subsidence, and diurnal Earth tidal movement caused by the Moon and the Sun. This daily movement can be as much as a meter. Continental movement can be up to 10 cm a year, or 10 m in a century. A weather system high-pressure area can hit a sinking of 5 mm. Scandinavia is rising by 1 cm a year as a total of the melting of the ice sheets of the last ice age, but neighboring Scotland is rising by only 0.2 cm. These remake are insignificant whether a local datum is used, but are statistically significant whether a global datum is used.
Examples of global datums include World Geodetic System WGS 84, also required as EPSG:4326, the default datum used for the Global Positioning System, and the International Terrestrial Reference System and Frame ITRF, used for estimating continental drift and crustal deformation. The distance to Earth's center can be used both for very deep positions and for positions in space.
Local datums chosen by a national cartographical agency include the OSGB36 by about 112 m. The military system ED50, used by NATO, differs from about 120 m to 180 m.
The latitude and longitude on a map gave against a local datum may non be the same as one obtained from a GPS receiver. Converting coordinates from one datum to another requires a datum transformation such(a) as a Helmert transformation, although insituations a simple translation may be sufficient.
In popular GIS software, data projected in latitude/longitude is often represented as a Geographic Coordinate System. For example, data in latitude/longitude if the datum is the North American Datum of 1983 is denoted by 'GCS North American 1983'.