Since the Marketplace isn't implemented in the Early Access of the game, I'll skip GDD n°12- Marketplace and go straight for GDD n°13 - Trade

At the end of the post you'll find a summary of the Early Access version status in terms of Trade.

Rationale

The idea is to allow the player to control their trade without too much micro-management, and allow trade to shape the galaxy map to create strong economical strategic points.

Trade Companies

HQ & Branches

Each player will have a limited amount of Trade Companies available to them throughout the course of the game, which will vary slightly depending on faction traits and research. To create a new company, a player will need to build an HQ as a system improvement on one of their systems.

To actually create a trade network, the player will then need to place Branches on other systems. The branches are placed using commercial ship and their fleet action, so you actually need to travel to the system you want to place the branch on. We define the following conditions:

• A single ship can only place a single branch
• A branch can only be placed on a friendly or neutral system
• The number of branches is limited at an empire level
• The number of branches depends on the number of trade companies, research, and faction affinities 

Placing a branch will then create trade routes between this branch and all existing HQs. Placing a new HQ will also trace new routes to all existing branches, but we don't trace routes between HQs (see "Tracing a route" for more details and schematics).

On top of these trade hard points (HQs and Branches), we define a notion of trade power that represents the global efficiency of a company, which can be improved on an empire level by building a repeatable system improvement (a finite number of times). However, to represent the logistics cost of managing several companies with potentially varying agendas, building more HQs (so founding more companies) will decrease each individual HQ's efficiency with each newcomer on the trade market.

A quick list to summarize the above:

• I need to build an HQ on one of my systems to found a Trade Company
• I then need to build a commercial ship to found a Branch
• I move my commercial ship to a friendly/neutral system to found the Branch
• A route is traced between my HQ and my Branch
• Any additional Branch will trace a new route to the HQ 

Upon placing a trade hard point, the immediate neighbors will also contribute to the trade income (see "Income - Hard point" for more details).

A captured HQ will be deactivated for the corresponding player. Any player can at any moment remove trade companies from their economy view, effectively destroying the corresponding HQ (for a price). In the case of branches however, they are destroyed upon capture by an enemy.

Tracing a route

Below is a series of schematics to illustrate how we plan to trace routes between HQs and Branches.

• A green node is a node that directly contribute to its hard point income (neighbor); which one is indicated by the colored outline
• Trade routes take the color of their corresponding branches 

First step is to build an HQ:

We can then place a Branch; the shortest route is computed between the branch and the HQ:

If we place a second branch, another route is computed:

Finally if we place a second HQ, two new routes are computed from the branches to this new HQ:

Income

Hard point

A trade hard point is either a Branch or an HQ. The income generated will be centralized on these systems, and modified significantly by the route's length. What contribute to the income is then:

• The hard point's system itself
• The neighbors of the hard point
• The length of the trade route 

The income will be  and  on one hand, and Luxury resources on the other hand. The FIDS part will be mostly based on systems stats, whereas the resources income will depend on the spatial localization (a hard point or neighbor needs to possess a deposit for it to contribute to the trade income).

All these incomes will be modulated by the route's length.

Systems on route

The systems on a trade route won't directly contribute to the trade income, but will benefit from being situated on one. Each node traversed by a route will receive a  and  bonus based on the system's development and modulated by the route's length.

Blockading

Blockade power

Who can say trade without also saying piracy? Any fleet will have a blockading power computed from number of command points, specific modules and possible faction affinities. This defines a max blockading power for the fleet, in % of leeched income from the trade route.

A faction fleet can blockade any hostile node that takes part in a trade network. The amount of trade leeched from the blockade will increment progressively per turn, until it reaches the max blockading power we computed earlier for the fleet. Players will also be able to hire privateers (mercenaries) from the market that won't show a specific ownership; using these units, they will be able to also blockade their allies or neutral trade networks without needing to declare war.

Hard point

Blockading a trade hard point (branch or HQ) will completely stop any route connected to it. The victim player won't receive any income from it, while the blockading player will receive up to their max blockading power in leeched income. As soon as the blockading fleet moves or is destroyed, trade will resume.

Systems on route

In the same idea, a player can block any node that is part of a route. In this case however, income is not completely stopped, only reduced by the corresponding fraction in blockading power. As above, when the raiding fleet moves or is destroyed, trade (and income) will resume at full capacity.

And that's all for now! I let you guys trade ideas!

[NDE: This last pun is entirely jhell's fault)

^I'm leaving this for posterity (as well as naming and shaming), next time you make puns, trade lightly!

HOW'S THE EARLY ACCESS VERSION ON THIS ASPECT?

HQ & Branches

• In the Early Access version of the game, there are no "commercial ships" to go and place the trade routes' hard points but this is subject to change.
• In the Early Access version of the game, branches can only be placed in the systems you own since they're placed by building improvement, but this point can be subject to the change of the point above.

Income

• In the Early Access version of the game, systems that are traversed by a trade route don't receive a Food income nor an Industry income

It still seems very opaque to me how much Dust the trade system generates. As an experiment, I took a turn 92 save with 14k income, 2.7k of which is reported to come from trade, and demolished all the trade HQs. There were 3 trade HQs at levels 5, 6 ,7 with 10 freighters each and 104% efficiency. The turn after, income dropped to 8.5k. What explains the nearly 6k discrepancy? It's hard to decide whether investing in the trade company and their infrastructure will be worth it currently because I don't exactly know how much dust will be made or how modifiers are applied other than to try to get the longest trade route running. Similarly, I'd also want to be able to know how the system generates extra luxury resources, as this can affect how I place subsidiaries in order to fund system developments.

Other points: I understand that this might be implemented later, but hopefully there will be a way to relocate a HQ after it's built without scrapping it and having to start from level 1 again. Borders shift, new settlements get built and I want to maximize income! Or maybe there are later techs that allow for extra subsidiaries, in which case this might not matter as much.

Also, is there any plan for systems that are not connected to the rest of the galaxy? I might avoid settling these if I learn that the gains from continuous trade routes are superior to their strategic location. Maybe these systems could get a build-able improvement that somehow links them to the trade network?

Edit: Upon investigating, I think I know why there is a discrepancy. Current laws were 'Excess Tithe' (+25% Dust), 'Fair Trade' (+20% Dust per trade company = +60) and the empire was Ecstatic (+50%). If these percentages are additive, then this adds up roughly to the 6k difference. It would still be more helpful if a breakdown of the modifiers to be applied to the trade income (and the resulting new trade income) was displayed on the Economy screen.