I am considering running a campaign in a modern city. It may be in an existing city or in a city of my own design. It will be a player-driven, "sandbox" campaign in any case. My problem is, how do I detail the playing environment in sufficient detail to account for anything my characters do? Tables and other ways of randomly determining various aspects of the setting like "Random Store" and Random Bystander". But I must have some things already detailed. So how much so I create? I'm thinking of creating a few nearby neighborhoods and then detailing a few important locations in each and coming up with a few "plots" that my players might get involved in. Anybody have a suggestions?