Civilization – the formula for city connection income

civilization-5

In Civ 5 connecting cities to your capital earns you income, but each road costs 1G to maintain, so you don't want to connect cities too early. What is the formula for calculating how much gold you will get by linking cities?

From my experience it seems to be related to the population of the cities, but there also seems to be a benefit to having lots of trade routes. So connecting a second city of roughly the same size seemed to give me more then double the income from a single city. I now have 6 cities in the "network" and despite them being farther away, my trade income is more than paying for the roads.

Best Answer

UPDATE The formula has changed as of the March 2011 patch, it is now

(city population * 1.1) + (capital population * .15) - 1 for each city connected to the capital, not including the capital.

  • The Machu Pichu wonder increases the modifier by 20%, to (city population * 1.3) + (capital population * .15) - 1.
  • Arabia increases the constant by 1, to (city population * 1.1) + (capital population * .15) (thanks WillfulWizard).

The economic overview also gives a far better explanation of how it is calculated - in other words, this question is now trivially solved by simply looking at that economic overview :)

Original answer below.

Okay, I did a bit more testing, and bwarner's answer is almost accurate:

Each city, excluding the capital, provides (city's population * 1.25) + 0.01 gold per turn. Owning the Machu Pichu wonder increases the modifier by 20%, to (population * 1.5) + 0.01, for all the cities.

The capital does not provide any gold.

The 1.25 and 0.01 can be seen in the Assets\Gameplay\XML\GlobalDefines.xml file:

<Row Name="TRADE_ROUTE_BASE_GOLD">
    <Value>1</Value>
</Row>
<Row Name="TRADE_ROUTE_CAPITAL_POP_GOLD_MULTIPLIER">
    <Value>0</Value>
</Row>
<Row Name="TRADE_ROUTE_CITY_POP_GOLD_MULTIPLIER">
    <Value>125</Value>
</Row>

The economic overview also demonstrates these values.

I couldn't find any other factor which affects these values, and I checked different difficulty levels, different distances between cities, different city route type (road vs railroad, road/railroad vs harbor), different city health and whether it is occupied. Looks like it's solely the population.

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