Hard to contribute something without visualisation...but let's try some thoughts, hoping they are what you are looking for.

• Adding additional commodities to round out production chains

We can make a commodity of every chemical element and base chemical compound (CH4, NH3, H2O, CO2, SiO2, FeO2, ...) depending on how detailed we want to model space mining and trade. E.g. "fertilizer" yet is a tailor made mixture of mainly Nitrogen, Phosphor, Kalium and other elements for different plants and environments.

Condition tags? Ok, let's list some natural resources on the bodies for the surface, crust, hydrosphere and atmosphere.

• Add a neighborhood context for condition tags (e.g. propagate the gas giant tag to starports on its moons).

Can be made, but even Hydrogen needs to be scooped and transported, and what about Venus and her CO2? => extended scoop equipment and even scoop missions?

Condition tags have to include type and intensity of energy sources (electric current from magnetic fields, wind, geothermal energy, solar radiation).

• Add a more intelligent system for selecting starport industries.

Ok, I appreciate your model as intelligent enough if it generates a starport in the orbit around Venus who processes CO2 from her atmosphere with H2 from the outer solar system to Carbon ore and plastics with O2 as byproduct, or even better imports H2O from ice moons to get the H2 from fuel cells because you can directly use electric current from more than 2000W/m2 solar radiation which is far more efficient than the 1340W/m2 we get in Earth's orbit. O2 may then be shipped back to the gas giants to be used in fuel cells, which could be another additional commodity. And oh yes, fuel cells are a source of energy to be tagged if no other source is available, meaning a demand for H2 and O2.

(Airships would be a better solution to scoop gas for permanent industrial supply, shall we model them as orbiting objects?)

We can make a commodity of every chemical element and base chemical compound

I appreciate the enthusiasm, but this is definitely not the direction we want to go. New commodities should be added because they fill a logical "gap" in a production chain or in commodity pricing, i.e. adding a "Chemicals" commodity produced at a refinery and consumed at a laboratory, or adding a high-value commodity to fill the gap between Robots and Precious Metals.

Can be made, but even Hydrogen needs to be scooped and transported, and what about Venus and her CO2? => extended scoop equipment and even scoop missions?

Adding additional mission types, equipment, etc. is decidedly outside of the scope of this PR. It is the underlying assumption of this economic simulation that this sort of NPC trade is happening "in the background", and making these equilibrium activities visible to the player is a different topic.

if it generates a starport in the orbit around Venus who processes CO2 from her atmosphere with H2 from the outer solar system to Carbon ore and plastics with O2 as byproduct, or even better imports H2O from ice moons to get the H2 from fuel cells because you can directly use electric current from more than 2000W/m2 solar radiation which is far more efficient than the 1340W/m2 we get in Earth's orbit. O2 may then be shipped back to the gas giants to be used in fuel cells, which could be another additional commodity. And oh yes, fuel cells are a source of energy to be tagged if no other source is available, meaning a demand for H2 and O2.

Condensing solid commodities from atmospheric gas is unlikely to be efficient enough to make a material difference to trade. Energy is not addressed by this economic simulation, as it is assumed that solar power and advanced microfusion using H2 provides more than enough power for industrial purposes.

For the most part, the complexity of simulation you describe above is not the focus of Pioneer. It can certainly be implied that all of this is happening in the background, carried out by the millions of people who inhabit star systems, but Pioneer is not a "tycoon" or economic-resource-management game and the player owning and managing a space station, etc. is a stated anti-goal of the project.

Here's the very short skeleton of the high-level design of this system for review purposes:

1. Conditions are a data-driven way for mods (and the base game!) to express named semantics about individual bodies. They are meant to eventually be determined at system generation time in C++. Because they have access to a random number generator, they can be used by more than just the economic system; for example, conditions can be used as a way to designate planets with valuable flora/fauna (for scanning missions), rare ores (for @impaktor's mining machinery) or any other kind of "planetary feature" developers/modders can think of.

2. Industries express the economic endeavors of a (logical) subregion of a starport. For surface ports, this is a number of buildings, for orbitals it's a chunk of the ring. Starports have a certain number of industry "slots" based on their population. Workforce is an abstract logarithmic quantity meant to express the amount of population required to operate an industry, but currently has no interaction with any of the systems in this PR.

3. Each industry expresses its production and consumption in a dimensionless logarithmic rate quantity called "flow". The rules for flow are simple, but intentionally inconsistent. An industry which produces a commodity with flow N can supply one other industry at that station with demand flow N, and two or more industries each with demand flow N-1. Two or more industries with supply flow N can supply a single industry with demand flow N+1, but can never satisfy an industry with demand flow N+2. The precise base of the logarithm used in flow is intentionally not defined, but varies from 2 to 10+.

   This "rule quirk" regarding industries satisfying N+1 demand is meant to provide a meaningful (if mostly invisible) effect to randomly generating multiple industries which produce or consume the same commodity at the same rate. Its concrete effect is that the rare station which consumes 6 flow of ore twice will have a higher sell price for ore than a station which only has one industry which consumes 6 flow of ore.

4. Flow is converted to a physical quantity via the supply/demand rates. The natural logarithm is used to determine how many discrete units of a commodity the station produces and consumes over an intentionally undefined period of time. Supply/demand rates determine the trade price of a commodity at a station, and are affected by the market's history value which records the player's interactions with the market.

5. All stations are assumed (currently) to be at an implicit equilibrium. This means that all commodity demand will be satisfied, regardless of how much of that demand is actually produced at the station. This is modeled via two mechanics: local and interstellar trade. Local trade allows any surplus flow (flow that meets or exceeds indigenous demand) from a nearby station to be consumed by the station with a deficit, and is imported at lower prices. Interstellar trade is the assumed source of the remaining deficit not satisfied by local trade, and is imported at significantly higher prices. Both local and interstellar trade are currently assumed to be happening in the background, and the responsibility for "visualizing" this process by instantiating NPCs is left to other modules like TradeShips.

Pioneer is not a "tycoon" or economic-resource-management game and the player owning and managing a space station, etc. is a stated anti-goal of the project.

As long as there are tradeable goods, you can play Pioneer in a "Transport Tycoon" or "Simutrans" mode...

Condensing solid commodities from atmospheric gas is unlikely to be efficient enough to make a material difference to trade.

Maybe it is if you don't have an Earth nearby full of accumulated fossil carbon - or maybe it is if you have an Earth nearby with a mankind who finally has learnt the lesson how to handle them wisely...

Demanding Efficiency would, in the end, mean that spaceports must be generated by an economy simulation code based on natural resources. Even the starports on earth are mostly at the wrong place.

To make suggestions for what you want: What is the wished and upper limit target quantity of industries and tradeable commodities? How are byproducts handled, means can industries have more than one commodity as output, more than two commodities as output, as rubbish as commodity yet exists?

To make suggestions for what you want: What is the wished and upper limit target quantity of industries and tradeable commodities? How are byproducts handled, means can industries have more than one commodity as output, more than two commodities as output, as rubbish as commodity yet exists?

The number of industry definitions has no hard limit. Avoiding too much granularity at this stage is desired (i.e. don't add a Mining Machinery Factory industry) as the industry system and number of discrete industries at a station are currently balanced around somewhat generic aggregations of multiple factories/companies/buildings into a logical "industry type".

As mentioned above, the number of commodities is something I'd like to avoid bloating, to keep each commodity feeling like it has an "identity" rather than disappearing into a sea of incredibly specific commodities. Additions for commodities should have a clear and defensible purpose.

Industries have any number of input and output commodities. Condition tags can be associated with modifiers to an industry's input and output commodities, which can increase and decrease commodity quantity and add new I/O commodities entirely.

I am happy with this branch as-is. I've addressed all of the TODOs I had, improved the selection process for starport industries, tweaked balance on commodity prices and flows, and added a new commodity, Chemicals.

Chemicals are used as an intermediate step between grain/carbon ore and medicines, robots, and more. They occupy the price point Industrial Machinery had prior, with both industrial and farm machinery receiving a large boost in price to match their relatively small supply and demand quantities.

This branch attempts to remain a balance between commodity price and availability, with more widely produced commodities receiving lower prices. Additionally, the changes to commodity restock and long-term effects on supply and demand mean that higher-priced commodities are not necessarily going to be widely tradeable in large quantities (though the effectively infinite nature of inhabited space does limit the amount of impact any one station's market will have on trade viability).

I will not expect a rigorous re-review. I intend to document the data formats introduced in this PR more thoroughly in a content-creation page on the devdocs, but I will not be waiting on that for merge.

! I intend to merge this PR no later than Friday, Jan 09 to allow adequate time for bugs to be found !

@impaktor this will likely be a headlining feature for the release notes with multiple points related to how the economy now works. Please ping me on IRC once you start drafting the notes and I'll try to write a player-comprehensible introduction to the economy sim.