You can associate vehicle paths with surfaces in certain CAD systems. This allows you to display and animate 2D and 3D paths on the surface rather than at level 0.
Existing Surface is only used by the Junctions module. Select from the drop-down list or use the Pick button to go to a drawing and select an object on the surface.
Final Surface is the surface onto which objects can be projected. Select from the drop-down list or use the Pick button to go to a drawing and select an object on the surface.
You can select Project Plan Onto Final Surface to display objects such as swept paths or roundabouts draped over the surface.