I agree completely with the comments above - this is sheer Hollywood stuff!!! One thing you might want to consider (something I read about in a mag about Japanese inventors' ideas, I forget what mag it was). Instead of putting a cop on every corner, the vision was to have an "automated" cop, a sort of stationary booth or column with surveillance cams, communications, and of course a nice friendly interface to help law-abiding citizens and tourists find their way about the city. It had a fancy japanese name, but was - inevitably - dubbed an "APM", or automated policing machine. Goes without saying that a version with self-defense capabilities was envisioned, too!