It was only a matter of time. I'm surprised I haven't yet seen an FPS based on public map data. As our phones and other devices increasingly serve as a window into a parallel digital environment, I think we'll see geography used as a standard reference bridge between a lot of other things. At some stage you'll be able to play top-down Zelda on your phone while someone else plays Doom, but you're on the same map, based on or generated from your local geography. Visual styles for each player will be more of a graphic filter than any fundamental difference in game mechanics.
I recently bought a Nokia mobile which came with a (fairly poor) top down racing game based on the built-in mapping and GPS.[1]
The premise was that you could race around the town you were actually in, but the sheer volume of mapping data meant you were effectively driving a little red car around some generic-looking, practically identical, streets and roads. There was no identity in any of the places. Micro Machines back in the '90s was much more entertaining!
I like the idea of it being more zelda-2 esque where once you go to a given town/location you are side scrolling. You could probably use most of the backgrounds/sprites from simons quest to get the desired effect for most of new york.
