Welcome to the Guild. For a modern city, just pick up a road map. Or if you want a lot of information on a major city that you aren't really familiar with, pick up a travel guide book. You'll get maps and lots of ideas for interesting locations and local color. Mapping cities is one of the hardest mapping tasks there is, so when you can fill your need with existing resources, it just makes sense. For on-line use, if your players need a reference, modern cities have maps online already, so you don't need to distribute anything.