It's different for every city. The Underworld is shape by different policies of the local government, community, police, and racketeers/crooks. Some things just hardly ever change and others will adapt to new policies. All respect to NYC for their reduction but their homicide rate wasn't nowhere near Memphis, Birmingham, nor JackTown.
If you think you are too small to make a difference, you haven't spend the night with a mosquito. - African Proverb