How does the trade network work?

[Malchar]

What determines when cities or resources are connected to the trade network? This seems obvious, but it sometimes resources right next to my capital are automatically connected as soon as I build the appropriate improvement on the tile. That is, I don't have to build a road at all. This might have something to do with whether there's a river there. Also, it seems like my cities will connect themselves automatically if there's a river between even if I don't have sailing. Some of these things might be messed up by various mods, but what is supposed to happen by default?

 

[Feyaria]

Rivers are connecting resources like roads. Sailing is only needed for trade routes outside your culture.

 

[Balnor]

If it's within your cultural borders, any clear open coastline or river will connect 2 cities in your trade network even without sailing (you might need fishing for coastal tiles, not 100% sure on that)
The same applies to resources, though you need a fort on the resource if you use a coastline to hook it up.

Sailing is just so that you dont need a cultural border anymore in between the two, though any hostile culture (barbs, civs you're at war with) in the way will still stop the trade.

 

[whats a navy]

There is a good guide in the strategy guides section of this forum. And for questions that are generally like this the war academy is great. It has plenty of articles discussing inner workings of the game and strategies. After reading through that whole chunk of guides I must have jumped one or two levels.

 

[kossin]

A few more references...

http://forums.civfanatics.com/showpost.php?p=7999426&postcount=76
http://forums.civfanatics.com/showpost.php?p=8005706&postcount=80
http://forums.civfanatics.com/showpost.php?p=7698429&postcount=7

 

[r_rolo1]

http://forums.civfanatics.com/showpost.php?p=7698429&postcount=7

IIRC this bug was solved already in one of the subsequent patches ( not sure though ). In spite of virtually harmless it was irritating to have it on game

Another tidbit of wisdow regarding this issue: river mouths act as harbors regarding trade networks . More on that in here ( it is on better AI mod forum, but the mechanic is the same than in unmodded BtS )