# Determine what coordinate system to use

A first step in planning a project is to determine what coordinate system to use.

## About this task

A coordinate system definition determines how to map and transform coordinates and, together with scale and offset factors, constitutes a spatial reference system.

## Procedure

Choose one of the following options:

- Use one of the predefined spatial reference systems. For a list of all available spatial reference systems, see view SYSGEO.ST_SPATIAL_REFERENCE_SYSTEMS.
- Create a new spatial reference system based on one of the more than 5000 provided coordinate
systems.
For a list of these coordinate systems, see view SYSGEO.ST_COORDINATE_SYSTEMS. Use the name of the desired coordinate system in procedure ST_Create_SRS to include the coordinate system information into the spatial reference system. The coordinate system is copied into the reference system, which then can be further customized with the ST_Alter_SRS procedure.

- Create a new spatial reference system with a customized coordinate system.
Use the procedure ST_Create_SRS to specify all required elements of the spatial reference system including the coordinate system definition.

The most commonly used coordinate systems are:

- GCS_WGS_1984
- Use this coordinate system when you need to define world-wide locations.
- GCS_NORTH_AMERICAN_1983
- Use this coordinate system when you need to define locations in the United States.
- UNSPECIFIED
- A default coordinate system for use when the coordinate system is unknown or you need to define locations that have no direct relationship to the earth's surface; for example, locations of offices within an office building or locations of shelves within a storage room.