Modern city map generator
I often use RL city maps. You're the GM, just tell the guy straight that the only connection between your city and any real city is the street layout, and even that may be open to change. Assert yourself! :)
You can make it a little easier by taking a city from some other part of the English-speaking world and transposing it into the area you want. It'll take him a long time to figure out even which city you're using.
I used parts of RL South Africa to represent another planet in a game once, and I've used RL Southampton, England, to represent... Southampton, Zombiefied England, without any problems from players.
A 'cease and desist' order from the GM (should it even prove necessary) is a lot less effort than designing a city from scratch, IMO.