According to the Roman Operating System there are four main elements that you will need to understand for the building, proliferation and networking of a city:
1. The city is comprised of standardized parts arranged on a matrix. These parts are the standard equiptment included in the container of each city and are easily identifiable.
2. The city is organized according to a series of general principles which are socially, culturally and politically determined, and in most cases are manifested in clear architectural and urban examples.
3. The city is the relationship of constantly chnaging flows superimposed onto a generic template.
4. You will have the ability to customize your city according to local topographical, climactic or cultural conditions.

For all its apparent complexity, once you know the rules, a city is easy to build.

--Taken from Mutations by the Harvard Project On The City--