I liked the way GTA-Like game on the PS2 was, based in london, modelled around some of the major parts of london.
I could sit there and know where to go, and what's the shortest route etc.
Surely it wouldn't be THAT difficult, if they were to combine work forces with some of the GPS Nav. Creators and use say Tom Tom map packs in-game so you could free-roam around specific places, i think that would be cool.