I will divide trade route system to 2 separate category. “Domestic trade routes”, and “international trade routes”
Domestic Trade Routes:
With domestic trade routes, we either share food, or production to the destination city.
To share food within trade routes with our own cities, we need a “Granary” in the home city(where we initiate trade with the trade unit)
To share production, we need a “Workshop” in the home city.
The number 1 in the Picture is sending +4 food to city of Colombo.
The number 2 is sending +4 Production.
In the above example, I am initiating the trade mission from the caravan in my capital. And, I’m making a food/production aid to the destination city, without losing anything from the capital (no reduction in food/production in the home city)
Strategy: For instance, we have built a new city, and it needs to make some buildings ASAP (building a wonder or an army). Then we can send a trade route to that city with production focus. Therefore it adds +4 production to the new city (which is a large production for a new city). Similarly, if we want a city to grow rapidly, we can initiate a food trade route.
The production trade route is extremely helpful when making wonders. They can speed up the production and production can end earlier
International Trade Routes:
International trade routes yield is mostly gold. And this gold income value changes with factors below; (you can also see in the above image)
Home City: Income, Buildings, Being next to a river
Destination City: Income, Buildings, Being next to a river
Additionally, the biggest factor is the number of different luxury resources we have with the destination country.
Trade route owner receives a large sum of gold, but destination country receives some gold as well.
In the image above, (in the red square area), the right arrows indicate my income, left arrows indicate destination cities income.
Also, there is a technology transfer exchange countries in trade. This technology bonus happens in both sides. The country which is behind in the research tree receives a larger bonus. And if the destination country doesn’t have any research that you hasn’t yet researched, (you have eclipsed them on researched), you don’t receive a tech bonus. When trading with city states, there is no technology exchange.
In the above image, it says I have 2 technologies that they doesn’t know. But I know every technologies they have researched. Therefore, I receive no tech bonus. But they receive +1 science bonus.
Strategy: If you can receive science from a foreign trade route, this means that civilization have technologies that you don’t have. With knowing this, you can choose which civilization you want to send your spy to, the higher the tech income from trade route means, it will be easier to steal a spy from that civilization.
Trade route ranges; buildings and technologies affecting trade route range
- Base range: 10
- With combustion technology +10 range
- Caravanserai building +50% range
- +50% range for arabs
- Base range: 20
- With compass technology +10 range
- Refrigeration technology +10 range
- With harbor +50% range
Note: Cargo ships move along the coastline before the astronomy technology. (They can move through oceans in your borders, or foreign borders that you have open border agreement.)
Therefore, after astronomy technology they can reach more cities as they move through the closest route.