Geodetic datum
![](/Images/godic/202501/15/Azimutalprojektion-schief_kl-cropped0234.png")
![City of Chicago Datum Benchmark](/Images/godic/202501/15/Chicago_City_Datum0234.jpg")
![Vertical datums in Europe](/Images/godic/202501/15/Vertical_references_in_Europe.svg0234.png")
![The same position on a spheroid has a different angle for latitude depending on whether the angle is measured from the normal line segment IP of the ellipsoid (angle α) or the line segment AP from the center (angle β). Note that the](/Images/godic/202501/15/Geocentric_vs_geodetic_latitude.svg0234.png")
A Geodetic datum or geodetic system is a coordinate system, and a set of reference points, used to locate places on the Earth (or similar objects). An approximate definition of sea level is the datum WGS 84, an ellipsoid, whereas a more accurate definition is Earth Gravitational Model 2008 (EGM2008), using at least 2,159 spherical harmonics. Other datums are defined for other areas or at other times; ED50 was defined in 1950 over Europe and differs from WGS 84 by a few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there.