In cartography, the Earth's shape has to be approximated: a reference ellipsoid
- • specify the Earth's radius and a flattening constant
- • different ones are in use
- • also called datum or geodetic system
- • for coordinates, a meridian (0° longitude) should also be specified
Important ones are:
- • WGS84: That's what GPS uses
- • OSGB36: That's what Ordnance Survey uses
- • ED50: That's what we use in most of Europe
