Workspace tab
Displays a hierarchy of the objects in the active workspace. A workspace is the subset of the active model database you specified when you started your design session. See What is a workspace? and Define a workspace.
You can select a coordinate system that is not an active object type, such as another system or part. Because the software filters the coordinate system list, only valid systems are available in the Coordinate System dialog. Invalid systems display dimmed.
Model tab
Displays a hierarchy of all the objects in the active model, including those that are not part of your workspace.
You can select a coordinate system that is not an active object type, such as another system or part. Because the software filters the coordinate system list, only valid coordinate systems are available in the Coordinate System dialog. Invalid parent systems display dimmed.
Expand to Current Item
Expands the hierarchy to display and highlight the current coordinate system. This option is only available if a coordinate system other than Global is active.