Trade restrictions

[MinnesotaRuss]

I am having trouble trading with some civs in my current game. I am on a continent with Norway and Jav. Washington and others are on a different continent. Until about ten turns ago, I was able to trade with only Norway and Jav. Now with Washington. But not with Georgia or any of the others even though I build a city not over 15 squares away. What gives?

 

[BarbarianHunter]

You probably need to "light up" some of the greyed out tiles between the origin city and the destination with units. Once the city center of the destination city is colorized you will fare better. The exact mechanics that are lost to me, ie. I am not sure as to exactly how much of the route's path must be "lit up" by unit(s) line of sight.

 

[Victoria]

15 tiles range that you have seen at some stage, so not line of sight but line of discovered land.
You can trade with the denounced, you just cannot get open borders with denounced, a reason to be peaceful for CV.
Trade is pretty simple in that regard, it is just the distance formula for finished trade routes and trading posts that are a bit insane, a trade route 4 tiles long takes nearly 30 turns to finish while one of the optimum of 10 takes 20. Atrader will bypass a trading post if it is one tile longer than the optimum path.

 

[playshogi]

So if 10 tiles takes 20 turns to complete, is there a table somewhere that gives info on number of turns each distance takes to complete?