Minecraft wiki entry for Building_a_metropolis, associated text: Crime City
Strictly enforced rules by police and admins.
Anyone caught committing a crime will be sent to one half of the city, while everyone else lives on the other side of the city. Separated by a wall.
Poorer people have to live close to the wall, while higher class people get to live in the nicer part of the city away from the wall.
Note: If you felt that you put too much work into your city to have riots, crime, and griefing on one half of it, this style of government is not ideal.