The question for this I have is what angle of perspective? Top view wouldn't be that good for detail, but a lower view would make it hard to do tall things...
I just got an idea: Instead of a map, what about a sky scraper? It could have a bottom made, and a default image of three levels of windows, and five or so windows wide. The images could then be three or so to a row, and they could stack and tile. This would cause the person who puts all the tiles to have a tad bit more focus on the tiles, but it would also allow for odd shapes, such as someone taking up a whole row.
People can then put things in the windows, or if they want change something on the outside, as long as it lines up with the others around it.