It depends on the level of detail you go into and how you generate your data. From Will's post, deriving your layout from OSM does seem to be a way of doing this to an extent, however if you derive anything from any other source you'll need to carefully check their licences very carefully.
There may be certain buildings or objects in real cities or locations that would require a specific licence to use (from past experience we've had to remove the odd distinct building that either didn't want to appear or had a ridiculously high licence fee), if you planned to try and actually use the real shops or corporate logo's of buildings you'd potentially have to obtain a licence for each one individually (this may vary depending on the country you're recreating).
As an example, take the Hollywood sign, if you wanted to put that in a game you'd need to specifically obtain a licence for it here.
As with all things legal, if in doubt, ask a lawyer who has some experience in this area.