When you open a feature source, you can override the coordinate system assigned to that resource.
To set coordinate system overrides
The coordinate system for the feature source are displayed in the table, including any overrides created previously.
To assign a coordinate system in which points are meaningful in relation to one another but do not represent single, absolute, fixed points on the Earth, select Arbitrary X-Y Coordinate Systems. For more information about coordinate systems, see Setting the Coordinate System for Your Map.
In the table under Set Coordinate System Overrides, the coordinate system you specified will be listed in the Override column.
To remove a coordinate system override, highlight the coordinate system in the table and click Remove. This will remove only the override, not the original coordinate system.