Ok then, for strat map models:
1st stage: Camp (yurts and simple adobe buildings);
2nd stage: Village (more buildings; and more elaborate ones?);
Bigger with wooden houses.
3rd stage: Town (buildings surrounded by a round mud brick wall, no more yurts; no towers in the walls?);
4th stage: City (squared city surrounded by a towered mud brick wall).
I reckon this will be enough.