With apologies for not quoting anyone, because its been over a full page since I last got to look at teh forum.
Re: vicki2 chocolate in your EU4 peanut butter. But... but... chocolate and peanut butter!
Using population for BT:
1) Trade and production cover most other sources of income
2) Most taxes in western europe during and even just before the time period were hearth taxes (based on #family domiciles) and goods taxes (frequently on things like salt, which tended to be regressive taxes in practice). Many nobles - the large landowners - were actually exempt from taxation in France at game start.
3) Urban populations produced much of the exploitable value for the crown, and generally had hearth or head taxes.
In short, population does directly relate to taxation, even in the time period.
As far as a modern game with the EUIV engine - it would be terrible, because modern infrastructure is so much more important than infrastructure in the period. But if you put a gun to my head and made me do it, then I'd do BT based on population, seriously jack up the cost and benefits of infrastructure (re: admin buildings), vary that cost based on population, and start western nations with much of the infrastructure already built. Then their effective tax would be a lot higher despite lower populations, representing the additional wealth their population has. Bangladesh could catch up and even exceed western nations if it can afford to build out the infrastructure, but that would represent turning Bangladesh into a westernized powerhouse with much higher standards of living. Of course, this demonstrates the limits of the EUIV engine to represent modern periods - governments don't control that kind of thing. Private enterprise commands vastly more wealth than any government, and this kind of economic development is not something that can just be fiated by governments. (They can do things which encourage or discourage it, but they can't just throw money at the problem and make it happen).
Re: scaling.
10,000 is not a very large city in 1444. A large city is like 50k people, of which there are plenty. Rome was a depopulated ruin in ~1444, with a population of 19k. OTOH, despite losing something like 2/3 of its population to the Black Death, Cairo still had well over 100k people. (Quite possibly 200k).
But we aren't talking about just a single city, we're talking about provinces which may have more than one city in them. The total urban population of a province could well exceed 50k or 100k even with no single city exceeding 10k. Any *province* with a total urban population of 10k or fewer should be 1BT.
At the same time, large cities were incredibly more wealthy than small cities. Wealth concentrates in large cities. Even using a *linear* scale might not represent the wealth advantages of having a large city adequately. The difference between a major city of 100k people and a 4k large village is certainly greater than a 25x increase in wealth. Now, relative size has some effect - wealthy individuals aren't going to move from Europe to Beijing readily, so being the largest city in Europe, or Northern France, will tend to maximize the agglomeration of wealth benefits from being large.
Now, the EUIV system imposes constraints. #1: BT can't be lower than 1. #2: there's some limit to province BT based upon warscore considerations. I'm not actually sure what it is, but more than 25BT in a single province would probably be too unwieldy to use. Accomodating possible events, set the top province at 22BT (Beijing). Set any province with 10k or fewer urban population at 1BT. We want a scale which isn't too far from linear, and then we want to boost the top regional cities a little bit to represent wealth attraction.
Actually, let's just use the largest city in a province unless there are two+ cities that are within the same (power of 2) order of magnitude, that'll make it vastly easier to calculate. (Or you can redo this chart once you know what the total urban population ranges look like for whole provinces summing up all cities - I just have individual city data to go off of).
Rough guess:
Code:
Urban Pop | BT
10k | 1
20k | 2
35k | 3
50k | 4
65k | 5
80k | 6
95k | 7
110k | 8
125k | 9
145k | 10
165k | 11
190k | 12
215k | 13
240k | 14
270k | 15
300k | 16
340k | 17
380k | 18
440k | 19
500k | 20
600k | 21
700k+ | 22
Then add 1 if its the largest city in its culture group.
Note: I'm assuming you're choosing a date 1600 or before. Once we start getting near 1700, populations start growing rapidly and this scale would be no good.
This still undervalues large cities, but it doesn't do so egregiously.