Editing Geodesy (section)

== Geodetic datums ==
{{main|Geodetic datum}}
{{further|Datum transformation}}

Because coordinates and heights of geodetic points always get obtained within a system that itself was constructed based on real-world observations, geodesists introduced the concept of a "geodetic datum" (plural ''datums''): a physical (real-world) realization of a coordinate system used for describing point locations. This realization follows from ''choosing'' (therefore conventional) coordinate values for one or more datum points. In the case of height data, it suffices to choose ''one'' datum point — the reference benchmark, typically a tide gauge at the shore. Thus we have vertical datums, such as the NAVD 88 (North American Vertical Datum 1988), NAP ([[Normaal Amsterdams Peil]]), the Kronstadt datum, the Trieste datum, and numerous others.

In both mathematics and geodesy, a coordinate system is a "coordinate system" per [[International Organization for Standardization|ISO]] terminology, whereas the [[International Earth Rotation and Reference Systems Service]] (IERS) uses the term "reference system" for the same. When coordinates are realized by choosing datum points and fixing a geodetic datum, ISO speaks of a "coordinate reference system", whereas IERS uses a "reference frame" for the same. The ISO term for a datum transformation again is a "coordinate transformation".<ref>(ISO 19111: Spatial referencing by coordinates).</ref>