Trade Routes

A late-game trading city with the Customs Ministry can produce as much dust as 10 other cities combined.

Trade Routes allow cities to trade with one another, generating Dust and Science income.

Mechanics

In order to create trade routes, Right of Way or Cargo Docks improvements must first be built, which connect cities by land or by sea respectively. Two cities are connected by land if they are in adjacent regions and both have Right of Way improvements. Likewise two cities are connected by sea if both have Cargo Docks and border the same body of water; note that this does not require the Docks to be built adjacent to the same named Oceanic region.

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.

Once two cities are connected, trade routes may be created between them. Normally a city can only create trade routes to other friendly cities; that is, cities belonging to the same empire, or to another empire at peace or in an alliance. The one exception to this rule is that a city is governed by a Roving Clans hero with the Black Marketeer skill can create trade routes to any other city regardless of diplomatic status.

Each city may create one trade route by default, with additional technologies and city improvements increasing this limit. Each empire capital also gains an additional trade route from the Palace building.

Each city creates its own trade routes independently, and trade routes are not bi-directional. That is, city A can create a trade route to city B, but B may not necessarily create a route back to A; and the trade route would occupy a slot in city A without consuming one of city B's slots. If a city has multiple possible choices for trade routes, it will automatically select the ones with the highest base / income.

For all intents and purposes, trade routes and all trade-related mechanics count as / income in the origin city without affecting the destination city in any way. For example, the Caravanserai only boosts income for trade routes originating in the city where it is built, and not for trade routes having that city as a destination. Likewise an empire only collects income from trade routes originating from its own cities, not from other empires' incoming trade routes.

The status of all trade routes in the empire is displayed in the Empire Management Screen (default keybind F1).

Formula

A trade route's base Dust and Science income is determined by the distance between the cities and the population of the destination city. This base value is then modified by a number of other effects, listed in the section below.

BaseIncome = 1 + 0.6 × (DestinationPopulation + 0.3 × TradeRouteDistance)

Yield = BaseIncome × (1 + TradeRouteBonus) × (1 + TradeRouteDustBonus)

Yield = BaseIncome × (1 + TradeRouteBonus) × (1 + TradeRouteScienceBonus)

Notes

1. DestinationPopulation does not include population from pacified villages.
2. The Grassilk booster is applied after the above formula: its bonus is not added to TradeRouteDustBonus, but rather it simply doubles the dust income from trade routes after everything else has been computed. This means that it is extremely effective at increasing dust income from trade routes.
3. Trade routes' / yields are considered part of the city's / income, so they are modified by city- or empire-wide bonuses like the Empire Mint or Museum of Auriga.

Trade Route Modifiers

There are many ways increase a city's trade route income, whether by increasing the number of trade routes or boosting their / yield. One unique mechanic, the Roving Clans' Inflation diplomatic action, reduces trade route income in another empire.

Name	Source	Description
Right of Way	Research Era II	A City Improvement which enables land trade routes between cities.
Cargo Docks	Research Era III ( Research Era II for Morgawr)	A City Improvement that enables sea trade routes between cities.
Palace	Empire Capital	A City Improvement that grants +1 additional Trade Route.
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 (Not available for Forgotten)	A City Improvement that gives +1 additional Trade Route and +50% Science from Trade Routes in that City.
Surreptitious Research	Research Era V (Forgotten only)	A City Improvement that gives +1 additional Trade Route and +50% Dust from Trade Routes in that City. Exclusive to the Forgotten, replacing the Scientific Envoy.
Customs Ministry	Research Era V	A City Improvement that gives +7 additional Trade Routes in that City. 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. 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. +50%/+50%/+100% Dust on trade routes in the city that the hero is governing.
Mechanical Exhibitionist	Vaulters Hero Skill	3 levels. +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.
Inflation	Roving Clans diplomatic action	-50% to targeted empire's trade route / income.

Secondary Trade Routes

When a trade route passes through multiple cities, all the cities between the origin and destination receive a small amount of bonus income, called a Secondary Trade Route. This income is a small proportion of the base income of the primary trade route and does not seem to interact with trade route modifiers in any way. And, 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.

Strategy

Starting from Era II, trade routes become a critical source of Dust and Science for almost every faction, with the income vastly exceeding earned from city tiles and/or population. Optimising trade routes is a great way to drive empire development as well as accelerate an economic victory.

The main reason why trade routes have such a high payoff is due to the way its multipliers stack. The following modifiers are all multiplied together:

• TradeRouteBonus (1.25x in the early game, 2.5x to 3x later)
• TradeRouteDustBonus (1x in the early game, 3x to +3.5x later)
• Grassilk booster (2x)
• All other bonuses to city Dust production. (1.15x in the early game, 2x to 3x later)

Additionally the Roving Clans governor skill "Black Marketeer", by allowing cities to form trade routes with any city on map, easily increases base trade route income by several times—not only because the cities are farther away, but because on higher difficulties AI cities tend to have much higher population. In this respect Black Marketeer is a catch-up mechanic that allows weaker factions to take advantage of the development of stronger ones.

Each additional trade route technology also has a similar effect by increasing the number of trade routes from a given city.

The general trend is that each new Research, Skill, City Improvement, Empire Plan bonus, etc... that is unlocked or built, when stacked with all the other bonuses, can lead to a significant increase in trade route income each time, making trade one of the fastest scaling sources of income in the game. By comparison, other sources of Dust and Science relying on tile yields, Population, do not have nearly as many multiplicative bonuses.

In the early game, it is recommended to recruit at least one Roving Clans governor in order to reach Black Marketeer quickly. At this point, the governor should be placed in a faction's capital, whose Palace building provides an extra trade route. Later in the game, the Customs Ministry should be built in a city at the very edge of the map in order to maximise trade route distance. With a Roving Clans governor and 9-10 heavily boosted trade routes, the city can easily generate more Dust than the rest of empire combined, and this is one of the most expedient ways to win an economic victory.