The location of a feature or observation is always expressed with reference to a specific spatial reference system that is of one of the following spatial system types supported by the Application Server: Geographic System, Projected System or Axis Reference System.

Based on these types you can define you own spatial reference systems.

The feature type defines which spatial systems types can be used to express the LSO of features of that type i.e. not all feature types allow to specify the spatial location of features in all of the types listed above.

The spatial reference system (and therefore implicitly the also the spatial system type) used to express spatial data is defined on creation of a new feature. Changing the spatial reference system for an existing feature is possible after the feature was created although restrictions apply - as described in following chapters.

If the spatial data support (defined by the feature type) is spatial data for observations all observations of that feature will use the same spatial reference system (and therefore of course the same spatial system type).