# Coordinate systems

A coordinate system is a framework for defining the relative locations of things in a given area; for example, an area on the earth's surface or the earth's surface as a whole.

Db2® Spatial Extender
supports the following types of coordinate systems to determine the
location of a geographic feature:

- Geographic coordinate system
- A geographic coordinate system is a reference system that uses a three-dimensional spherical surface to determine locations on the earth. Any location on earth can be referenced by a point with latitude and longitude coordinates based on angular units of measure.
- Projected coordinate system
- A projected coordinate system is a flat, two-dimensional representation of the earth. It uses rectilinear (Cartesian) coordinates based on linear units of measure. It is based on a spherical (or spheroidal) earth model, and its coordinates are related to geographic coordinates by a projection transformation.