Used to assign the GCS of an attached reference to the active model. You can use references to orient your active model when the attached reference has a standard GCS specified and has not been scaled or rotated, or when a reference with a computed Azimuthal Equal Area GCS is attached without scaling (it can be moved and/or rotated).

If a geographic coordinate system, with an attached reference, has a geographic referencing mode turned on, the reference cannot be used as a source for the GCS. Its position is calculated from its GCS and the active model’s current GCS so selecting it as a source will not change the current GCS. The Comment column provides the reason a particular attachment cannot be used as a GCS source.