Hell, the entire North and South shores are also infested. Every time an empty lot(s) gets torn up you can see the little bastards everywhere in the neighborhood. They live in every empty or abandoned piece of property in Boston and it's suburbs. They live in burrows on empty land or abandoned industrial sites.

I grew up in Buffalo and they are endemic there too. My theory - totally uninformed, just a guess, is that any place that had water traffic has rats. I don't remember Denver having this many - although I haven't lived there in 20 years.