Variation in spatial reference systems

Geoids in common use

Table 3-2: World Geodetic Standards

Reference Ellipsoids:
Name Equitorial (major) axis in meters Flattening (1/f) Region
Airy 1830 6377563 299.325 Great Britain
Bessel 1841 6377397.2 299.153 Central Europe
Everest 1830 6377276.3 300.80 Indian subcontinent
Clarke's 1866 6378206.4 294.98 North America
Clarke's 1880 6378249.2 293.47 Africa; France
Krasovsky 1940 6378245 298.2 ex-Soviet Union
World Geodetic System 1972 6378135 298.26 NASA, US Military
GRS 1980/ WGS 84 6378137 298.257 GPS, new systems

These reference ellipsoids may serve as the best fit to the actual geoid in different parts of the world. A horizontal 'datum' adopts a reference ellipsoid and locates geodetically surveyed points on that ellipsoid.

Projections in common use


Table 3-1: Common projections used as GIS spatial reference systems
worldwide Universal Transverse Mercator (6 degree strips)
United Kingdom National Grid (transverse Mercator)
Germany Gauss-Kruger (3 degree strips)
Switzerland National Grid (Gauss-Kruger)

State Plane System (USA) [North-South states, e.g. Illinois two zones] France 'Grille Lambert' three zones

State Plane System (USA) [East-West states, e.g. Washington two zones] Malaysia (peninsular) Malayan Skew Orthomorphic (oblique Mercator)
State Plane System (USA) [Alaskan Panhandle; oblique Mercator]