Available map overlays are as follows:

Terrain - colorized terrain

States - black outline of state boundaries

ARTCC - tan outline of Air Route Traffic Control Center boundaries

VORs - yellow triangles of the VOR aides to navigation that appear on the advisory plotting chart

Airports - light blue diamonds of the major airports

TWEB - orange lines representing the Transcribed Weather Enroute Broadcast routes

Maps are forced on top with the exception of the color terrain which is initially placed underneath the basemap (the state outline). By clearing the terrain checkbox and then checking it, the terrain will be placed above the basemap but below all other overlays.