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.
About this task
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. Several spatial
reference systems are already provided by the database to cover commonly used
coordinate systems. If none of the available systems are appropriate for the data,
you can create one that is.
Procedure
To decide whether to use an existing
reference system or create a new system:
 Answer the following questions
to determine whether you can use one of the existing spatial reference
systems.
 Does the coordinate system on which the existing spatial
reference system is based cover the geographic area that you are working
with?

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:
 Review the information in Conversion factors that transform coordinate data into integers.
 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.

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.
 If the existing spatial reference
systems do not work with your data, you need to create a new one.
What to do next
After you decide which spatial reference
system you need, you specify this choice in spatial functions
or procedure calls.