There are probably as many cities as you can travel. I think I proved that it's randomized not by seed but something else.
Cities are chunk based spawns every time you load a new chunk there is a chance that a city will spawn provided that there are no other cities within a certin distance center to center. The curent distance is set to 1000 blocks so with the cities being 480 blocks you must travle at least 520 blocks away from a city befor finding another city