Cargo

Cargo is a Resource produced by Caravanserai and Docks. Production of Cargo is unlocked by the Knowledge Portage.

It is used to generate trade routes between your Territories, which enables you to transfer Resources between them.

Later on in the game, once you have unlocked the Knowledge Coinage, and have the Coinage policy enabled, you can create routes between other players you have a Trade Treaty with.

Resource :

Cargo Costs
Each Resource has its own cargo cost per unit transferred.

Here is a chart showing the cargo cost per unit of the resource

Cargo costs are multiplied by the average distance between source city, destination city and cargo city.

In the below example, a trade route between the RED cities has a distance of 6. If cargo is provided by either city the cost factor would be 6+6/2=6. If the cargo was provided by the PURPLE city, which has a distance of 3 between both, the cost factor would be 3+3/2=3.