*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.