In what is simultaneously the best and creepiest marketing stunt I've seen in a while, Ubisoft has built its own public database on real world cities, in a similar vein to Watch Dogs' depiction of Chicago. WeaAreData won't let you hack traffic lights mind you, but does offer a surprisingly comprehensive breakdown of census data for cities it does cover. Currently, that's London, Paris, and Berlin. No word on whether or not there are plans to expand.
As it is, you can check out breakdowns of the three cities including: CCTV camera locations, train schedules, ATM locations, crime and unemployment rates, as well as neighborhood resident's average monthly salary.
So yeah, creep to your hearts content.