I have created a utility to create the Topdown texture from the MaskMap. You can just drag the .track file to the shortcut or run CreateTopdown and open the .track file. It reads the .track file for all the overlay textures and then builds the topdown using the MaskMap as a guide on where to place and blend the textures. You can then either use it as is or render it.
Caution: It will overwrite the topdown texture that it creates. It names the topdown the same as your MaskMap texture and appends "_Topdown". So if your MasMap bmp is called track_detail.bmp, this utility will create/overwrite track_detail_Topdown.bmp.
In order to use this you need to set Overlay_Base, Overlay_R, Overlay_G, and Overlay_B textures in your .track file.
Download here: Setup_CreateTopDown_v102.zip
v1.0.2 has a fix dealing with quoted file names when drag/drop is involved.
If your track folder is inside your "Program Files" folder and you are using Vista/Win 7 then you need to go to the properties of the shortcut, click on the compatibility tab and check the "Run As Administrator" check box.
Sample MaskMap from Valley Ride:
Sample Topdown generated from the MaskMap:
Go here for info on Create Topdown.