How does TRADE work in the game?

[Foz]

Hmm. Maybe I'll mod my game so the wharf series grants export lines like the port series does. It seems like it should be more important than the port series somehow. Oh wait, I can't, because whatever mechanic currently causes export routes isn't the trade_fleet one, and therefore isn't in the EDB at all that we know of. Gravy.

I don't suppose anyone has seen anything in any of the game files that tells the game ports should be giving export routes, have they?

If not, then maybe I will assume it's based on the level of the port. If that is the case, a semi-solution might be to integrate the wharf buildings into the port line for cities.

The port series builds in 2/3/5/6 turns, granting 2/3/4/5 trade bonus. Costs are 800/1600/3200/6400.

The wharves OTOH are 3/5/6 turns with 2/3/4 bonus for 1600/3200/6400. So they're nearly identical to the 2nd, 3rd, and 4th buildings in the port series, just with 1 less trade bonus in each case. It probably makes the most sense to insert them just before the port building with the same build time, then, as a sort of stepping stone to the better building. So the new layout would be:

Port/MerchantsWharf/Shipwright/Warehouse/Dockyard/Docklands/NavalDrydock

Which yields costs, build times, and trade bonuses like this:
800/1600/1600/3200/3200/6400/6400
2/3/3/5/5/6/6
2/2/3/3/4/4/5

I've bolded the port series buildings and their stats, while underlining those of the wharf series.

As always thoughts and ideas are welcome - I wouldn't be posting otherwise!