- one quarter of the town is for common laborers and food providers;
- one quarter is for necessary craftsmen;
- one quarter is for merchants and/or nobles and any others who control the town;
- one quarter is for whatever the town is notable for: a town with a strong academic interest will have a scholar's quarter, which could also contain a temple district; a town with mining interests will have a quarter devoted to refining, working with, or trading in metals.
Each quarter might actually be larger or smaller than others; they do not have to be literal quarters, just conceptual quarters. Each quarter can be divided into four border districts around a central core, and the contents of each district can be based on what the district is bordering; thus, the temple district in a scholar's quarter might border the central hub, to make general access easy, or the merchant's quarter might contain a petty merchant's district that border the commoner's quarter.
The "thieves' quarter" will probably be a district in the commoner's quarter, in whichever position seems like the least desirable. In a really corrupt city, the entire quarter might be considered the thieves' quarter, with one district being considerably rougher than the rest.