It's a complete mystery to me.
It is pretty simple:
- Game Concept "Domestic Market" itself is explained in Colopedia.
- Mouse over a single Unit or a look in its Colopedia will tell you what Yields it wants. (Different Units want different things.)
- Mouse over the Yield Icon (in the 2 Yield Rows) will tell you the accumulated Domestic Demand (and Price) for that Yield in that City.
- Market Buildings are needed to unlock Domestic Market feature (Higher Levels give higher Domestic Demand / Consumption.)
Now all you have to do is to manage your production and transportation to always have the Yields in the Cities as their Citizens demand.
Then they will be automatically "sold to the colonists", which will produce Gold and Happiness.
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There is nothing myserious about it.
1. Look at the City which Yields is wants.
2. Bring those Yields to that City or directly produce them there.
3. Those Yields will be sold there and your Colonists will be happy.
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Does it need some micromanaging?
Sure. It is the most micromanaging intensive feature in the mod.
Does a best "golden strategy" exist? No it does not.
I purposely assured in the design that such a "one way to win" does not exist.
Every map, every starting location, every colonial empire you build looks differently.
Take a look at the numbers in your cities and adjust your production and transportation accordingly.
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Whenever e.g.
Coffee is getting low in your
Beer-City, you need to bring new
Coffee to it.
And while you do that you can grab as well some
Beer to bring it to your
Coffee-City.
And maybe the
Cigar-City is
in the middle of those so when passing by you also grab some
Cigars (for the others) sometimes or drop some
Beer or
Coffee.
And maybe just 2 turns and a
Wagon Train with
Wine will arrive in the
Cigar City so you can pick some of that up as well for the
Beer-City and
Coffee-City.
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Now multiply this
"mathematic problem" with
52 Yields or
potentially 96 yields after my "Yield Explosion".
Do you really expect to simply click a button and the
game playing itself for you?
The mathematic problem I describe here is
multitudes more complicex than e.g. finding the
optimal moves in chess.
(Many more variables and much much more dynamic every turn.)
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This feature is designed as a
"mathematic puzzle" and
challenge for the brain.
It is a
mini-game in itself which needs
great skills to be mastered.
You
simply need to take a bit of time to
micro-manage.
There is
no "magic button" to automate this feature.

(Everthing you could try to automate would be worthless a few turns later.)