So, we have our first 9th level character. He’s established a domain and has been getting population increases through agricultural investments.
We’re kind of stuck on Market Size for the villages. As the domain populations are domain-wide, it’s hard to say where everyone actually lives.
I’m tempted to say, most settlements will remain as villages and Market Class VI until an Urban Settlement (10,000gp) is developed within the domain. But, I’m not sure.
So, how do you determine when a Market Size shifts since populations for domains are determined by domain instead of by settlement.
I would argue that any market worthy of a class is actually an urban settlement, with the remaining population being peasants working the land in small, insignificant communities. You’ll notice in many of the tables that describe settlements, the very smallest settlement will have an *asterisk next to it denoting that “A Class VI market will exist at the domain’s stronghold only.”
However, if it’s very important to have a market class ahead of time, consider using the table “Placing Villages, Towns, and Cities” section starting on page 231 of the core rulebook. Use the “Desired Urban Demographics” table in reverse and compare it to how your player’s realm could accurately be described, and then use that to determine the likely urban population and the largest settlement.
Chances are that your PC has settled a wilderness domain, or at best a borderlands domain, which means you shouldn’t be shifting down too many columns, but the best case scenario for a domain with less than 3,750 families (which presumably your newly minted 9th level player has) would be a large village of 250-449 people if you had an “Advanced, Urban Realm” with a “Centralized Settlement Pattern”.