The issue with mapping a city and determining real values is all based on what type of city you are making. To build a city in a fantasy world would indicate a different set of values due to the possibility of magic or just a different concept of how things should flow together. To model a different race or culture on a middle age European design seems absurd. Also you are assuming human baseline technology. Also perhaps a dictator requires building codes that would have never existed. The options are endless and to apply real world limitations on a fantasy world is kinda silly unless that is the style you want.

I do agree that most cities should be built small then expanded based on growth much like Cyotemax did on his town.