Honestly, I wouldn't like a city map as I think it would be implemented.
Can you imagine the pain in the ass of making those buildings scalable by battle armor? Giving them nooks and crannies to hide in? Yeesh!
What I'd suggest instead is a sprawling military base. That way, you can place mech-scale structures and open things up so that these structures aren't just big blocks of obstruction. Like hangars, give them catwalks for BA to walk on and make them tall enough for mechs to pass through. Better yet, make them short enough for light mechs to pass through, but not larger mechs. See what I'm getting at? You have a much greater deal of leeway in regard to fine detail when creating structures built for the vehicles we use rather than using structures that would be found in a city environment.
