I am trying to understand whether you need to settle a city directly on a tile with a river in order to get river bonuses (the extra trade for example) or if it is sufficient that the river tiles just exist within the city radius? Basically, if I find an area with a lot of river tiles, but I don't want to settle my city on one of the river tiles, does the city still get bonuses as long as the river tiles are still within the city radius?