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

When you plan a project that uses spatial data, you need to determine whether any of the spatial reference systems available to you can be used for this data. Answering the following series of questions can help you decide whether to use an existing spatial reference system or create a new system.

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?
   2. Do the conversion factors associated with one of the existing spatial reference systems work with your coordinate data?
      The offset values and scale factors defined in the spatial reference system are used to convert the coordinate data that you provide to positive integers. To determine if your coordinate data works with the specified 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 existing 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.
   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 create a new one.