![geodetic datum geodetic datum](https://gssc.esa.int/navipedia/images/2/29/Datum.png)
Geodetic field operations are conducted on this surface. The true shape of the Earth is generally perceived as the natural surface of the Earth, i.e., the continental surface and idealized equilibrium sea and lake surfaces. The shape of the Earth can be defined in a number of ways.
![geodetic datum geodetic datum](https://i.ytimg.com/vi/J3_SVXm0Fio/maxresdefault.jpg)
Theory of the Earth’s shape (theory of the Earth’s gravity field) provides the basis for determining the geodetic datums. This chapter mainly discusses geodetic datums and the methods, principles, and plans for establishing geodetic control networks. The missions of constructing geodetic datums include determining and defining the coordinate system, height system, and gravity reference system, and establishing and maintaining the coordinate framework (horizontal and satellite geodetic control networks), elevation framework (vertical control network), and gravimetric framework (gravity control network). Again, it is geodetic datums that are referred to when the spatial positions of geographical features in the real world are expressed in the data space. Geodetic datums provide initial data for all kinds of surveying and mapping work and serve as the foundation for determining the geometric shape and spatial–temporal distribution of geospatial information. Geodetic datums consist chiefly of coordinate datums (including classical horizontal datums and three-dimensional coordinate datums), vertical datums, sounding datums, as well as gravity datums. To measure terrain, surface features, position coordinates, heights, and gravity values at points on the Earth’s surface, there need to be corresponding reference points or surfaces (also known as datum points or surfaces), namely geodetic datums, to which surveying and mapping results are referred.