I also plan to create whole town maps that feature sites from the Haiku of Horror series. I also need a map of my capital city (which I'm putting off at the moment, because I plan to create a city of at least 100,000 population) and that will be one big, time consuming map to create. (Having created Kasai, the capital of Minkai, for Paizo's Jade Regent adventure path with a population of 30,000 approx - I know the work that's involved for such a map.)
While I see your point of the 3 major areas - I still intend to cover all areas simultaneously, as many socalled rural locations can still fit in an urban location. Farms do surround cities, for example.