Where they go and where their from:

After looking into Rikers prison history I started to focus in on the "Million Dollar block." A million dollar block is a neighborhood or block with enough imprisoned residents that one million dollars or more is being spent on prison costs. The cost of imprisonment is so high that it takes surprisingly few imprisoned residents to reach the million dollar mark, spawning the related "five million dollar block." In a million dollar block, more government resources may be spent on imprisonment than any other social or public services, raising a number of questions in extremely poor and crime-ridden neighborhoods.

The concept of the million dollar block emerged in 1998, when researchers in NYC began mapping incarcerations block by block, creating a visual representation of the number of people on watch block who were in prison. They identified a number of hot spot neighborhoods, where large numbers of former residents were in prison, and started calling them "million dollar blocks." By looking at these blocks, a number of trends of have been identified; such as a large number of citizens below the poverty level, along with a high number of minorities.