I am planning to release a videogame with a map based on the real map of a city (or part thereof) based on the Open Street Map. It would also include Open Street Map in the game, almost certainly modified. Open Street Map as a tiled map is released on CC SA BY which is compatible with GPL 3. I want to release my game on GPL 3. But there's a problem - Open Street Map as a database is released on Open Data Commons Open Database License (ODbL). This license is share-alike which means I would have to release any derivatives under the same open database license. As far as I know GPL does not allow additional restrictions placed on the released content, and I'm not sure whether I could even release parts of the game (i.e. code and most assets) on GPL and then the map on ODbL. Even if that was ok with GPL, if my work would be considered as a derivative of the map then I would still be bound to release the game on the database license which is unacceptable and also doesn't make any sense.
Can I include Open Street Map (MODIFIED - it's important as the license places the restrictions explicitly on modofied derivative works) in a game released on GPL 3 (or GPL 2) for that matter? Am I required to release any game that includes OSM through Open Database License?
edit: How I use the Open Street Map data --- the map itself (in tile form, released under CC-SA-BY also) as a map (in fragments) of the environment, in addiction the layout of the buildings, streets etc. all serves as the basis (trying to keep it accurate but for obvious reasons it's impossible) of the game map as it takes place in a certain real (postapocalyptic but that's irrelevant) city. So I tried to model specific places, streets and such from the map to specific places in the game. Also I thought it would be a good idea to use the street map (perhaps after some graphical tinkering) as the game's map as it would be both accurate and already done.