I do not want to ask about an explanation of the city and trade network in general, because it has been explained quite well in the Civilopedia, let alone it is rather intuitive.
But there are a couple of issues/situations where the factual state of affairs cannot be explained via the Civilopedia.
- Why on the image below the capital has the rice resource, though they are placed on the different rivers. No road is present. The sailing has not been discovered yet.
The civilopedia does not mention a requirement for resources to be on the same river, but it does this for cities:
cities on the same river are linked together as long as the river between them stays in your borders or in neutral territory
- The second issue is that, when another civilization from a different continent establishes a contact with me I can have trade routes to its cities, though I do not have yet any visible pass on the map to that civilization. But every so often I have no trade routes with such civ, until I sail with a fishing boat or another vessel to that civ. Sorry I do not have an example right now, and the Worldbuilder is to buggy with trade routes to create such an example manually now.