[Twan]

I think that terrain types should have an effect on population growth (say farmlands +0,2, plains/forest +0,1, swamp -0,1, waste -0,2, freshwater +0,1, with fort +0,1 ; or something directly based on supplies) as well as the actual population (something like province with 30k+ pop -0,1, province under 5k +0,1, province under 2k +0,2). Say you control a farmland province which has lost much of its population. The 1k remaining people have lots of rich lands to exploit, logically their number should grow fast. In the other hand I don't think that 35k guys trying to survive with the rare supplies of a waste should have an automatic growth.

But I don't really think it's worth the effort to implement this kind of system, and without it having just the effects of the growth scale is better than an arbitrary automatic growth.