When rivers divide cities why is that the money is often in the north

Question

eg London, Bristol

Answer 1

because trolls live below the bridge

Answer 2

i would imagine it has something to do with the river's direction of flow... this might be important bc it affects the efficiency and effectiveness of trade... i'm kind of guessing here, but it seems to make sense to me. what do you think?

Answer 3

Same thing for the equator.

Or ... maybe the threats (from other human tribes or from wild animals) generally came from the south, and the river was a protective barrier.