Trade Routes 101

[Foxhawk]

Could someone explain trade routes in their entirety, if it isn't too much of a bother? How does CIV4 determine what cities you trade with, how much you make, etc etc.

[Silver14]

Supposedly they always take the best routes available. The number of routes depends on your tech, civics, and some wonders.

I havn't a clue what determines how much you make although I'd wager it depends on how much commerce both cities invovled have and the distance between the two cities.

I'm in the camp thats glad it is totally automated, i'd rather not have to manually create the trade routes.

[MadDjinn]

I somewhat agree with the idea of it being automated, but I've seen plenty of my cities staying internal (and low income) even though it would be better to make external trade routes (all requirements also being met)

[rjmatsleepers]

Re: Trade Routes 101

Originally posted by Foxhawk
Could someone explain trade routes in their entirety, if it isn't too much of a bother? How does CIV4 determine what cities you trade with, how much you make, etc etc.

The size of the trade route appears to depend on the size of the cities rather than on their commerce. A foreign route has a minimum size of 2. I understand that the value of a route may be affected by distance, but I cannot confirm this. For foreign trade, only one city in your empire can trade with each foreign city. If there are not enough foreign cities available for trade (trade requires "open borders" and a route IIRC), your cities will trade amongst themselves. Multiple domestic routes are allowed. The available trade routes are allocated to your cities in what the program considers the best way.

A harbour increases the value of a trade route. It also causes a reallocation of routes which can result in the gain from a harbour in city A being counteracted by a loss of a route in city B.

The number of routes can be increased by technologies (Currency and Corporation), Wonders (Great Lighthouse), Civics (Free Market) and buildings (airport). I believe it can also be affected by UN resolution (Single Currency). The Free Trade resolution may make more valuable routes available, although this depends on the game situation.

RJM

[Blake]

Trade route value is tied closely to population, mainly the population of the distant city. A forigen size 15 city is going to create a pretty valuable trade route whether it goes to a size 4 or size 12 city.

Trade route allocation is based nearly entirely on the population of your cities.
The biggest cities get the best trade routes (highest gold value).
There is one important modifier: The Harbor DOUBLES the effective population of a city for purposes of attracting trade. A size 10 city with a harbor will attract better trade than a size 19 landlocked city.
Ties are broken by city age, so if your (original) capital and another city are both size 10, the best trade will got the capital.

That really is most of the strategically useful info.

[Foxhawk]

so how does it determine the eligilibility of a city to trade with another city? Must the cities be connected land to land via roads or shore to shore via ocean (does there have to be a path?), or can a landlocked city trade with a city on another island? etc.

[Tau Ceti]

Generally, as long as you have a trade route (the three arrows in a triangle next to the leader's name) with another civilization, all your cities can trade with its cities. The route can be via roads, rivers, coast or (after Astronomy) ocean. But if only one party has Astronomy and the only trade route is via ocean, they are the only ones who get the trade. You also need open borders, unless the open markets UN resolution has been passed.

[Foxhawk]

Sounds good. Thanks, guys.

[Blake]

It is also possible to trade without the arrow-triad, for example if you have sailing and scout along the coast, running into another civs city. You can trade with that city even if you don't have the arrow-triad with the civ itself.

To be honest I'm not exactly sure how it decides when there's a complete trade route between two civs. I know that one civ scouting an unbroken trade path to the other civs capital will do the trick, and under some cases each civ can scout part way. I THINK it's enough for each civ to scout out a trade path to half way, but each civ needs to be able to trade along that path - like even if between both players an unbroken stretch of coast has been scouted, both players will need sailing in order to fully form the trade link.

[rjmatsleepers]

In the following save, I have open borders with Elizabeth and the trade network symbol appears by her name, but there are no trade routes. Can anyone tell me why this is so?

I am using some non-standard XML, but I don't think this should make any difference.

RJM

[Thedrin]

I can't look at the save at the moment but there may be a simple reason; is the save taken from the first turn in which both requirements were met? In my experience trade routes don't appear til the next turn.

[rjmatsleepers]

Originally posted by Thedrin
I can't look at the save at the moment but there may be a simple reason; is the save taken from the first turn in which both requirements were met? In my experience trade routes don't appear til the next turn.

That's an interesting possibility, but in this case, it is not the turn in which both requirements were met. In fact, I previously had trade routes with Lizzie. The above save is from the auto save. In the real game, Lizzie closed her borders shortly afterwards - I'm not sure if that is significant.

BTW, I have seen cases where the new trade routes appear as soon as the open borders are agreed rather than on the next turn and in the above save, if you close borders with Mansa, the trade routes go straight away.

RJM

[Blake]

I havn't looked at the save but typically the "trade triad but no routes" thing is caused by the AI having a connection to you, but you not having a connection to them. Most trivially this is caused by Sailing/Astronomy, however there are a few other ways involving tile visbility and such. Another way is war. If the trade connection goes through a 3rd party, then that 3rd party can stop trade in one directions, or both directions if both civs are at war with the 3rd party.

[rjmatsleepers]

Originally posted by Blake
... typically the "trade triad but no routes" thing is caused by the AI having a connection to you, but you not having a connection to them.

That's a very helpful comment, but in this case, there appears to be a road link between my capital and Lizzie's capital that doesn't pass through anyone else's territory. (And we're not at war.) I'm feeling baffled.

RJM

[zeace]

If Lizzie switches to Merchantilism, then she gets no foreign trade routes. One of the patches fixed it so that if she can't trade with you, you can't get trade routes with her either.