Trade Routes allow a city to trade with another connected city, generating 
Dust and 
Science income.
Creating Trade Routes[]
The first step in creating trade routes is to research Imperial Highways or Cargo Docks. These technologies allow the Right of Way or Cargo Docks improvements to be built, which allow cities to be connected by land or by sea. Two cities are connected by land if they are in adjacent regions and have both built the Right of Way improvement. Two cities are connected by sea if they have both built the Cargo Docks improvement in the same body of water. Note that this does not require the Docks to be built adjacent to the same named Oceanic region. Additionally, if two cities are connected by land or by sea to a third city, then they are also connected themselves. This means that two cities may be connected via a complicated series of alternating land and sea routes passing through multiple cities.
Note that only cities within your empire and friendly cities (that is, cities belonging to empires that are either at peace or in an alliance) may be connected. Alternatively, if a city is governed by a Roving Clans hero with the "Black Marketeer" skill, then that city may be connected to any other valid city, regardless of diplomatic status.
Once two cities are connected, then trade routes are established between them. By default, each city may create one trade route, and each capital may create two trade routes due to the Palace, though this number can be increased by some city improvements. If a city is able to create multiple possible trade routes, then the one(s) that generate the most Dust and Science will automatically be selected.
The city creating the trade route is called the origin, and the city which it connects to is called the destination. Empires only receive income from trade routes originating from its own cities, but not from trade routes originating in other empires and connecting to its cities. Additionally, most trade route bonuses apply only to the origin city or empire. The base Dust and Science generated by a trade route is determined by the distance between the two cities and the population of the destination city. However, trade route bonuses generally only apply to the origin city; for example, having a Caravanserai in a city only improves the trade routes originating in that city, but not the trade routes having that city as a destination. See the Calculation section for more details.
You can check the status of all trade routes originating in your empire in the Empire Management Screen (default keybind F1).
Improving Trade Routes[]
Once trade routes have been established, there are a number of ways to increase a Trade Route's output, as well as the number of Trade Routes a city can have. All of these methods are listed below, but it should be noted that some of these methods have effects beyond what is described here - such as additional Upkeep costs from City Improvements.
| Name | Source | Description |
|---|---|---|
| Negotiation Tactics | Era II Legendary Deed Reward | A City Improvement that grants +50% Trade Route Bonus on City Trade Routes. |
| Caravanserai |  Research Era III |
A City Improvement that grants +1 additional Trade Route and +50% Dust from Trade Routes in that City.
|
| Scientific Envoy | Research Era V |
A City Improvement that gives +1 additional Trade Route and +50% Science from Trade Routes in that City. Not available to the Forgotten.
|
| Surreptitious Research | Research Era V
|
A City Improvement that gives +1 additional Trade Route and +50% Dust from Trade Routes in that City. Exclusive to the Forgotten, and serves as a replacement for Scientific Envoy.
|
| Customs Ministry | Research Era V |
A City Improvement that gives +7 additional Trade Routes in that City. This improvement may only be built once in an Empire. |
| Well of Dust | Roving Clans Faction Quest | A City Improvement unlocked by completing Chapter 7 of the Roving Clans faction quest that grants +2 additional Trade Routes in that City. Requires that Right of Way be built in the city first, and that the city has an income of at least 100 .
|
| Safe Passage | Roving Clan Hero Skill | 3 levels. +25%/+25%/+50% Trade Route Bonus to trade routes in the city that the hero is governing. |
| Fast Trader | Roving Clan Hero Skill | 3 levels. +1/+1/+2 Dust and +50%/+50%/+100% Dust on trade routes in the city that the hero is governing.
|
| Mechanical Exhibitionist | Vaulters Hero Skill | 3 levels. +1/+1/+2 Science and +50%/+50%/+100% Science on trade routes in the city that the hero is governing.
|
| Black Marketeer | Roving Clan Hero Skill | Allows trade routes to be made with factions that the player is at war or cold war with, for the city the hero is governing. |
| Commercial Agreement | Diplomacy | Increases the Dust gained from trade routes with the targeted empire (+1% each turn, up to 20%). Only available between factions that are at peace or in an alliance.
|
| Research Agreement | Diplomacy | Increases the Science gained from trade routes with the targeted empire (+1% each turn, up to 20%). Only available between factions that are at peace or in an alliance.
|
| Improved Trade Routes | Empire Plan - Economy and Population level 3 | +50% bonus to trade routes. |
| Grassilk Booster | Luxury Resource | +100% Dust on trade routes for duration of booster.
|
| Cargo Nexus | Unique Facility | +5% bonus to trade routes, with +1% additional bonus per Fortress controlled by the empire. |
Secondary Trade Routes[]
When a trade route passes through multiple cities between the origin and destination, all of the cities in between also receive bonus income based on the main trade route. This is called a Secondary Trade Route. While a city may be limited on how many primary trade routes it can create, it can have an unlimited amount of secondary trade routes passing through it. Secondary trade route income is determined only from the base income of the primary trade routes passing through a city. Additionally, none of the trade route modifiers affect secondary trade routes.
Calculation[]
The Dust and Science yields for a primary trade route are computed using the following formulae:
yield = (1 + 0.6 × (DestinationPopulation + 0.3 × TradeRouteDistance)) × (1 + TradeRouteBonus) × (1 + TradeRouteDustBonus)
Notes[]
- DestinationPopulation does not include population from pacified villages.
- The grassilk booster is applied after the above formula: its bonus is not added to the TradeRouteDustBonus attribute, but rather it simply doubles the dust income from primary trade routes after everything else has been computed. This means that it is extremely effective at increasing dust income from trade routes.
- For all intents and purposes, a trade route's final income is considered a part of city income. This means that it is modified by city-wide or empire-wide percentage bonuses such as the Empire Mint.
- The +1/+1/+2 Dust bonus from the Fast Trader hero skill and the +1/+1/+2 Science bonus from the Mechanical Exhibitionist hero skill are currently not implemented. (The percentage bonuses from those skills still work correctly, however.)