Questions about "trade" in Shogun 2

[RedKnight]

Some things involving trade are very clear, but other ideas, I can't figure out... let me toss out some ideas, and see if anyone can help.

What does it mean when e.g. a Warehouse says its effect is an "increase to trade income (tariffs only) by +30%". If I play Chokosabe and own the whole island of Shikuko, all trade seems to come my capital Tosa, but Tosa can't have Warehouses... does that mean that Naval Tradition (and Warehouses) everywhere on the map are useless for me, for increased Trade income? (On what info pane can one see increases to trade income? It would be hard to discern on the Trade pane... is it buried there somewhere?)

What is "improves export capacity (increases trade values) by +80" for a Trading Port? Again - is it useless if it's not Chosokabe's capital? (other items such as the ability to build ships, aside)

I thank you kindly in advance if you can shed light on these issues.

Your future shogun,

RK

[Nowake]

Salut Chevalier Rouge! (I'm sorry, I know I should abstain, manners and all, but it's the partial french title of a book that was read to me as a child and I couldn't help myself; RedKnight keeps a hint of a bloody undertone, yet that is so completely lost once translated in french /tease)

Regarding Warehouses. Warehouses increase the income of the sea lane connected to the province's port. If there is a sea lane. Sea lanes have certain values, depending on the type and quantity of goods being sailed back and forth. If you build a warehouse, the tariffs on those goods increase by 30%.
You can check the value of tariffs in the Finance > Trade section; there is a list with the items being traded with each clan, and in the specific row of each clan, to the right of the item you export towards that clan, there's an icon that stands for the tariffs you put on those goods -- once you mouse over that icon, the exact sum provided by the tariffs is revealed.
From what I've seen, the real question is, in fact, how to establish those sea lanes.
Which becomes consequently, how to divert trade towards the most profitable ports.
To take your example, you write all trade is being directed to Tosa. First of all, your naval trade exports are directed through the ports closest to the province producing the goods from what I've observed (except the goods acquired by occupying a Trade Post, those seem to be traded from your capital); meanwhile, naval trade imports are all directed to the port closest to your capital. Now, the main sea lane connecting Shikoku to the outside world does not have to begin in Tosa's ports. If you leave the naval infrastructure underdeveloped in Tosa (you do not build a Trading Port), all your maritime trade will have to pass through the closest province's port. So you can actually ensure that port is always situated in the province which benefits from Naval Tradition. Even if you do build a Trading Port in Tosa, if you are able to actually export/import beyond the capacity of said port, the rest will be diverted towards the nearest port. The same for Warehouses situated in other provinces. As long as the ports in the province where you build your Warehouse are the closest ones to provinces where goods you export are produced, they will become the outlet for those goods.
It must also be noted that, besides the normal trade flow fluctuations -- your commercial partners can be conquered, they can break trade agreements, the route can be blocked on either end, raided all over -- the most frustrating part comes when you lose a trade agreement; if they begin exporting the goods you were providing from another, even upon the reestablishment of trade, the sea lane may not be reactivated.
Another annoyance: sea lanes do not change depending on the position of raiding or blockading navies (actually, unsure about the latter, I was never put in a position to test it).
The idea is to divert naval trade through your most sophisticated customs-tax collecting ports, I think (unsure about the correct economic terms there, I'm romanian so I may gum up the works sometimes).

improves export capacity (increases trade values) by +80
The goods you produce are priced per unit and traded away through a sea lane connected to the nearest port, as I wrote above. In the absence of a land route of course. The increased export capacity simply raises the trade values of each of the goods traded through that sea lane by 80, provided you are able to export enough units to take advantage of that.

And, seeing as I reached this thread after reading your previous one in the CA section of the Tea House, I might have an answer for the question econ raised there:

I don't understand the idea of provinces with "high value trade goods" - can anyone explain this and how to inspect it in game?

Trade goods are produced in units, and prices per unit for each can be viewed in the Finance > Trade section. Say you produce Horses, the price per unit for Horses is 25. You produce 3 units, so you are able to export Horses worth 75. To this initial value of 75, you apply tariffs and get the final value of the exports towards a specific clan (later, to this you add a perk coming from a long trade relationship). Anyway, there are differences between the price per unit for goods, provinces which produce stone provide a higher income than provinces which produce timber.
Yet I think you want your metsuke placed in the province with the port through which the goods are traded, if they are traded through a sea lane, not the one producing it, despite the fact that the province producing the goods benefits from a fixed Commerce-classified revenue increasing with each level of the building producing the items, which is there to simulate customs revenue. Of course, on many occasions, they coincide, especially when you speak of "high-value" goods i.e. Craftworks, which are decently priced, can all be found in provinces with access to the sea. Quick look: http://shogun.bitcrumbs.com/ and mouseover the craftwork icon at the bottom of the map.

[RedKnight]

Hi Nowake,

Sorry for taking so long to reply... you have written a lot of good info, but it is taking me a while to work with it... I am mainly playing the game, and changes in trade can take days of play IRL to see major changes. Still, I am seeing things with new eyes, thanks to your help. It will probably be a while until I feel like I understand trade well. In the meantime, let may I say a few things?

You noted all the problems with how trade can change over time, and be hard to manipulate. But the worst one is, how all trade ends with Realm Divide

improves export capacity (increases trade values) by +80: The goods you produce are priced per unit and traded away through a sea lane connected to the nearest port, as I wrote above. In the absence of a land route of course. The increased export capacity simply raises the trade values of each of the goods traded through that sea lane by 80, provided you are able to export enough units to take advantage of that.

Are you sure that you mean prices here, and not capacity (number of units)?

One big problem (perhaps) with Chosokabe, is that there isn't a Naval Tradition province anywhere on their home island of Shikoku. I am still trying to figure out if this means that they can never take advantage of Naval Tradition, anywhere.

When you talk about tariffs on trade, is it particular to imports or exports? And, I assume that Trading Posts work quite differently from trade with other clans. (It continues past RD.)

Is there any way to see more information on tariffs, than with the Finance / Trade / individual trade partner's tariff amount? It's really intriguing that you said metsuke might be better placed in the Naval Tradition province dealing with an actual good being exported. (Right? Tariffs are all about exports?) But is there any way to gauge this? I don't think I can see anything about tariffs on a given province's info screen.

Thanks again for all your help! Plus, if you're Romanian, your French is even better than my native English! Except I'd like to be called Chevalier Rogue, not Rouge - thanking you kindly.