A District Pass allows citizens of Romerus City to traverse the districts freely. All citizens born in the city are confined to their district of birth until they apply for a District Pass. Citizens who move into Romerus City from the outside are confined to the district they are approved to move in to.
A citizen must apply separately for each District. The hardest district to receive approval for is, of course, the Noble District. Citizens born in the Low-Town District tend to find it much harder to get approval for District Passes.
The District Pass is not an actual physical object. Instead it is attached to a person's identity, as are many things in the world, such as bank accounts. Enforcers can check if a person has a District Pass by doing a brief retinal scan.