I'm wondering what defines part of a city. I am playing as Russia and I have 6 cities in two groups (there is only one tile separating the two, but it never wants to expand there). I have a great merchant and I want to build a customs house on a river. however I think that this river is between 4 different cities. The real question is, what cities do I receive benefits from?
If one city has every building possible (bank, market, stock exchange) and the other one is a brand new one (but still connected) which do I receive the bonuses from? Do I get bonuses from both? Does it gain bonuses from ALL connected cities? Or does it only gain bonuses from the city whose citizens work it? Suppose it's equidistant from both cities; what would happen then?