Calculating World/City/Town/Village/Hole-in-the-ground Demographics

[Genth]

I'm building up the information for a large, homebrewed setting, and I need some help calculating the (magical) demographics. There are some helpful resources I've found like http://www.lucidphoenix.com/dnd/demo/ however these seem to be tailored to the 'official' DnD standard, whereas my setting is a little different. For example, there are, with only a couple of exceptions, no characters in the world above Level 10. (and in fact one of the primary reasons I want to get some help for demographics is so I can figure out what magic items might be available where.)

Any ideas?

[Yahzi]

no characters in the world above Level 10.
I have an worldbook dedicated to that very issue. You can download from the RPGNow link in my sig (it's free). I am working on an updated version, but the essentials remain the same.

Essentially I treat peasants as a source of XP; thus, rulers are higher or lower level based on how many peasants they rule. By turning XP into an economic resource instead of an imaginary ad-hoc substance, you can make sensible societies mechanically, instead of having to make up each one from scratch. (How many paladins does the Temple of Bob have, and how do you make that match the number of wizards in the Evil Tower, where both sides are supposed to be relatively equal?)