Trade basics

[SlowThinker]

1. I am behind DaveV in the HoF voting . I tried to bribe MPers but it has no effect. and Straybow wrote in his vote: 'DaveV (Many contributions to GL)'
2. This forum seems to be unloved
3. I always missed a thread about trade basics. Samson and solo published some very advanced points, but when I played ELG #2 and neededed to take care of trade I had to study trade basics myself. I noted my remarks and now I added some tests and tried to summarize trade basics. I would like if experienced traders can read and correct this text.

[SlowThinker]

Terms

One-shot delivery bonus
A civ that delivered a caravan obtains gold and beakers (in case of a commodity caravan) or half of the food box is filled in the target city (in case of a food caravan).

Trade routes and ongoing trade bonus
Each city handles a list of outgoing trade routes. (They are shown on the city display.) There may be max. 3 routes on the list. There are two types of trade routes: commodity routes and food routes.
Commodity routes:
Each existing route brings the ongoing trade bonus: gold for the source city. It also blocks the corresponding supply of the source city (if on the supply list).
The routes don't bring any asset to target cities. They only may block their corresponding demand commodity (if on the demand list)
Food routes:
A food route brings +1 food per turn to the target city and -1 food per turn to the source city.

BTA (base trade arrows)
A city property. BTA = arrows from city squares minus corruption (so arrows from trade routes don't count)

S&D trigger
Some actions work as S&D trigger of a given city: all S&D values of the city are recalculated (using formulas discovered by samson) and so the S&D lists may change.
Then proper S&D comodities are blocked (put in parentheses); let us say the city name is XY:
1) all the blocked supply and demand in XY is unblocked
2) supply of all existing caravans homed in XY is blocked
3) supply of all outgoing routes from XY is blocked
4) demand is blocked: Civ2 checks all outgoing routes of XY and their target cities (max. 3). These target cities have outgoing routes (max. 9) and just these routes block coresponding demand in XY. (In other words: in order to have a Wine demand in York blocked there must be any city with a Wine route to York AND there must be (any) route from York to this city)

These actions are triggers:
* a new trade route (primary or secondary) - in the source city of the route
* help wonder - in the source city
* the 16-turn solo cycle (on the assumption that the city window is opened - note: but this not always true. Dye/copper bug?)
* any more?

These actions are not triggers:
* origination of a caravan
* delivery of a caravan (this fact causes commodities is "limbo" status)
* city foundation (a city S&D list may change if a caravan is delivered in a new city immediately. But how is determined the S&D list before the delivery??)

---

Actions

Origination of a caravan
If a caravan is built then the corresponding supply is blocked. No supply is blocked if a caravan is bribed.

Loss of a caravan
Disbanding from a city window (home city or a city where the caravan is stationed): the supply is unblocked
Disbanding by giving an order to caravan, killing: nothing happens (the supply is not unblocked).

A caravan may be delivered or it may help to build a wonder:

Delivery of a caravan (commodity or food)
One-shot caravan delivery bonus: gold and beakers are obtained (in case of a commodity caravan) or half of the food box is filled (in case of a food caravan).
If a caravan of city A is delivered to city B then the Civ2 engine tries to establish two trade routes:
a primary route (A is the source city, B is the target city; the comodity of the caravan is used)
a secondary (opposite) route (B is the source city, A is the target city; one of the three supply commodities of city B is used)

Rules are identical for both a commodity (primary and an secondary) and food routes:

* Trade route may be established only if a route of corresponding commodity to the target city doesn't exist yet. (Therefore on the list of trade routes the routes always differ in a commodity or a target city. You have never two identical routes (city+commodity) in the city window)
* If the city has one outgoing food route then no new food route may be established.
* If there are less than three outgoing routes from the source city then the route is always established and is added to the end of the list (except it would be 2nd outgoing food route).
* Otherwise the Civ2 engine tries to find a route that is 'not too much better' than the new one and to replace it. It looks the 'route quality' is based on 'quality of target city', i.e. on BTA of the city. BTA of target cities of EXISTING routes are halved and rounded down, then compared with BTA of new target city (it looks foreign BTA are doubled and different continents have no effect - BTW this is in accordance with rules for route value (ZERO trade). But this requires more testing).
If BTA of new target is equal or better than worst BTA/2 of existing cities then the route is replaced and it occupies the slot of the replaced predecessor in the list of outgoing routes.
If there are several 'worst' routes then the first one in the list (the topmost in the city window) is replaced.

An establishment of a new trade route works as a S&D trigger.

Secondary (opposite) trade routes
The Civ2 engine tries to establish it in accordance with general rules of trade route establishment (this happens also if no primary route originates).
If the opposite route is established then its commodity is chosen automately by the Civ2 engine:
If there are any commodities that aren't blocked then Civ2 choses among them accidentaly. If all 3 commodities are blocked then a route is established too and the commodity is chosen accidentaly from these blocked supplies; this way one supplied commodity may be unblocked (if 2 routes with equal commodities to different cities originate).
Civ2 always prefers a commodity that is demanded in the target city, but only if the commodity is not blocked in the source city (if blocked then the demand in target city has no effect).

First the commodity of the trade route is chosen from the original supply list and only then the S&D trigger may change the S&D lists. Therefore the new route may block no supply.

Food caravan
A food caravan is always available.
A city may have only one outgoing food route (if one outgoing food route exists then all next food caravans never create a route (even if they go to high-arrow cities) and fill the food box only)
The 'not better too much better' rule for route replacement is identical to commodity caravans.
No secondary route is done.
Food caravans are never established as secondary routes of commodity caravans.

'Help wonder' caravan
A commodity or a food caravan may be used (no difference). The WoW needn't to be ever finished, just the disband of caravan's shields into a city that builds a wonder works.
Neither primary nor secondary route is established, but still it works as a S&D trigger in the source city (no effect in the city that builds the wonder) - so called 'wonder bread'.

---

Remarks

Blocking supply
The lists of blocked supply commodities (commodities that are in parentheses) may be changed in 2 cases:
* if a commodity caravan is built in a city (not bribed) then the corresponding supply is blocked
* after any S&D trigger (see the part about S&D triggers)

So there may be three reasons why a supply is blocked:
* A caravan holds that commodity. Solution: deliver the caravan and get into situation 2. or 3.
* A corresponding trade route exists. Solution: replace the route by a new one (primary or secondary)
* The supply is in 'limbo status' (this happens if you deliver a caravan and no route is established; no route means no S&D trigger). Solution: you need any S&D trigger: establish any new route (primary or secondary) or help a wonder (so called 'wonder bread') or wait until next 16-turn solo cycle.

Free routes - routes that don't block a supply:
* food route
* route whose supply commodity has been changed to another one
They are very valuable and should be preserved.

Blocking demand
The lists of demand supply commodities (commodities that are in parentheses) may be changed after any S&D trigger only.
See the part about S&D triggers and realize this: if you deliver a demanded commodity then the demand in the target city is blocked iff both the primary and the opposite routes are established.

[Straybow]

Yeah, yeah... whine away... you'll get in...

4) demand is blocked: Civ2 checks all outgoing routes of XY and their target cities (max. 3). These target cities have outgoing routes (max. 9) and just these routes block coresponding demand in XY.

So if York makes a Coal route with Tokyo, and Tokyo says it has a Beads route with York, the commodities of the other two routes from Tokyo can block demand in York?? Crazy!

"Help Wonder"
Is this triggered when you disband in the Wonder producing city, or when the Wonder is built? I.e., can you set production to WoW, disband caravan/freight, then switch production to a regular city improvement (maybe after first closing the window)?

[SlowThinker]

First I must say I am not sure with my statements. They should be verified.

So if York makes a Coal route with Tokyo, and Tokyo says it has a Beads route with York, the commodities of the other two routes from Tokyo can block demand in York?? Crazy!

Noo. Only the routes from Tokyo that go to York block the demand.
But imagine what can happen:
First Tokyo delivers Wine to York and a route is established. There is no Wine demand in York so no demand is blocked.
Later demand in York changes and Wine is in demand. Then York makes a Coal route with Tokyo, no opposite route is established, but the old Wine route wakes up and blocks the demand in York.

"Help Wonder"
Is this triggered when you disband in the Wonder producing city, or when the Wonder is built? I.e., can you set production to WoW, disband caravan/freight, then switch production to a regular city improvement (maybe after first closing the window)?

Yes, you can switch the production. All you need is one tech that allows to build a wonder.

Could you rephrase my sentences so that they are more clear?

[SlowThinker]

This is not true:

Originally posted by SlowThinker in the main text
it looks secondary routes never block demand in target
cities

It was in my old version and I forgot to delete it.
Secondary routes work exactly as primary ones.

BTW .. concerning terms ... 'wonder bread': do you call this way any 'help wonder' delivery or only those that unblock a demand? Does it signify you feed the wonder or the unblock?

[SlowThinker]

Originally posted by SlowThinker
Could you rephrase my sentences so that they are more clear?

I tried something, pls check if it is more clear now.

[Elephant]

I've always considered "Wonder Bread" as an unblocking trick, because there's no "wonder" (ie- amazing effect) if I'm just using it to get shields to start an improvement. The "Bread" part signifies that it usually comes from Food caravans - real commodities are too useful elsewhere, but might be used if the city is critical like the SSC.

[SlowThinker]

I awaited some feedback...
In past I didn't understand when commodities are blocked/unblocked. The text should explain it, but I am not sure if it works as described.