Objective of the game is to put police men in the street in a way that every street is protected by cops. A street is safe if a cop can see it. Also, to be easy on the budget in economical hard times, you have to use as little cops as possible, e.g. no cop is allowed to see another cop, since than some street parts would be protected by too many cops. Some buildings have special requirements as they might require a specific number of cops right next to the building (or in some cases no cops are allowed next to specific buildings). A number in the building indicates how many cops have to be there, if there is no number, any number of cops is ok.