How does TRADE work in the game?

[Foz]

Foz: I think export only takes one of the fleets of the exporting cities, and trade routes aren't two-sided (so you can have cities that export to a city but not import from it and vice-versa). This would make sense because you can only export specific resources.

Is there no difference then between "export routes" and "trade fleets available?" The chart Sapi posted (by ArchieGremlin) says that the Port series gives the former, while the Merchant's Wharf series gives the latter. It's been my experience that building the Port series gives smaller boosts to trade (though still better than land usually) while the Merchant's Wharf series gives absolutely HUGE boosts to my sea trade. I was rolling with the assumption that they are in fact two different things.

In fact I would've said I think the following:

Export route - a single resource trade route, exported to the most profitable place. Agreed these are one-way. I'm not sure each is for one resource only, but that's been my impression.

Trade fleet - gives a full trade lane with another settlement, the two then exchanging all possible resources (i.e. every resource the other does not have). IMO this would be the only way to explain the massive numbers of resources I usually see being traded by sea on the trade details scroll - it's generally WAY more than how many exports I'd be allowed. It's not entirely clear if they go both ways.

So that's what I've been assuming is going on...