All depends what you mean by an urban area. Basically, if an area isn't fit for a cat to live in, it's not really fit for a human being to live in. And there are plenty of urban area which fall into that category. (Like all rules there are probably some exceptions to that. I just can't think of many. Human beings are like rats - we can survive in situations which aren't at all good for man nor beast. And as with rats, the result isn't pretty.)

Cats don't crap on doorsteps. They've more sense of decorum than that. Not unless they are trying to tell you something.