Geographic Coordinate System From Reference Dialog
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.