Something similar is already possible with splitter. You can create an *.osm file with many polygons inside, each with tags name=* and mapid=* (see attachment). splitter will give you tiles with 6234xxxx and per polygon a <name>.args with list of necessary data tiles per map. That args-file you can hand over to mkgmap for creating the map. It's pretty useful if you create many maps at one time. Gerd coded it a while ago for my usecase, but as far as I remember it's not documented. But if your map areas are overlapping you will get some very small ones, which looks strange. But of course that's just a optical issue and of course depending on the overlapping. As I'm using this approach, I haven't thought about let mkgmap calculate a smaller map, as I just would have add another polygon to my osm-file in that case. Henning