*18. November 2007*
**Coordinates **are variables from
the analytical geometry to describe positions in a coordinate
system.

**Coordinate Systems** are geometric
structure elements and reference systems for coordinates.
Special coordinate systems are used in describing mathematically shape and size of geodetic
earth models or in map
projections.
**Coordinate Reference Systems **are
coordinate systems in combination of a spatial datum to
describe spatial position through spatial coordinates.

**A spatial datum** describes the
position, size and orientation of a coordinate system regarding to
the physical or geographical earth.