“Geodesy is the science of studying the dimensions and the form of the Earth as well as its gravity field. Its principle objective is to develop terrestrial reference systems that any user or georeferenced data creator can access (…). The adoption and implementation of such reference systems are an indispensable tool for the standardization of geographic information and for positioning in general ” (source: http://geodesie.ign.fr/).

See also: Coordinates (System of), Projection (System of)
[French: Géodésie]