Hehe... hitting that sign makes a huge difference Thank you so much, also for your detailed explanation of calculating it! I think I got it now A pity I can't award reputation yet.

I excluded castle, temple and river while counting only buildings within the city walls and ended up with 302 acres -> 66 people / 1 acre. Metropolis would'nt be the right word for Merridia, but it still would be a large town/small city according to the guide. Not really what I imagined
I'm thinking about simply increasing the number of inhabitants.

Some research results (Wikipedia hooray!):
Cologne (1500): 40.000 - biggest city in germany
London (1500): 125.000
Hamburg (~1500): 20.000
Lübeck (1502): 25.444
Nürnberg (1485): 36.000

As with about 42.000 inhabitants Merridia would be a "large city" following the guide, that's my choice The wards outside the city wall will be built quite loosely.

I will go on with drawing the buildings