# Deciding whether to use an existing reference system or create a new system

Answering the following series of questions can help you decide whether to use an existing spatial reference system or create a new system.

After you determine what coordinate system to use, you are ready to provide a spatial reference system that suits the coordinate data that you are working with. Db2® Spatial Extender provides five spatial reference systems for spatial data.

## Procedure

To decide whether to use an existing reference system or create a new system:

1. Answer the following questions to determine whether you can use one of the existing spatial reference systems.
1. Does the coordinate system on which the existing spatial reference system is based cover the geographic area that you are working with? These coordinate systems are shown in Spatial reference systems supplied with Spatial Extender.
2. Do the conversion factors associated with one of the existing spatial reference systems work with your coordinate data?
Spatial Extender uses offset values and scale factors to convert the coordinate data that you provide to positive integers. To determine if your coordinate data works with the given offset values and scale factors for one of the exiting spatial reference systems:
1. Review the information in Conversion factors that transform coordinate data into integers.
2. Look at how these factors are defined for the exiting spatial reference systems. If, after applying the offset value to the minimum X and Y coordinates, these coordinates are not both greater than 0, you must create a new spatial reference system and define the offsets yourself. For more information about how to create a new spatial reference system, see Creating a spatial reference system.
3. Does the data that you are working with include height and depth coordinates (Z coordinates) or measures (M coordinates)?
If you are working with Z or M coordinates, you might need to create a new spatial reference system with Z or M offsets and scale factors suitable to your data.
2. If the existing spatial reference systems do not work with your data, you need to Creating a spatial reference system.

## What to do next

After you decide which spatial reference system you need, you specify this choice to Spatial Extender in functions or procedure calls.