I am also wondering if these maps that the kids would be working with, or creating, would be of the existing town or something that they would be making up and develope through the software. If it is of the town, you could start with a basic background, and do a drag and drop with various elements that are provided by the software. This could be usable in both of the cases that I mentioned before, with the background and elements differing (as needed) for the various stages of developement.

I am not a real programmer, but this sounds like it could be done with a browzer program hosted locally, with a light sensitive/touch screen and stylus. Have the kids draw the roads where they think they should go, and then place the buildings and such and at the end do a comparision with the actual. This last bit would only work with the real town, and could use a video intro to the stage they would be working on.

I wish you success and much enjoyment with this. Let us know which way you decide to go and how it turns out.