I'm creating this post to explain the functionality of trade routes in this mod, which is substantially different from the way they work in vanilla.

I rebalanced the values according to the principle that, in trade one always needs to give something to get something in return. It doesn't make sense for a trade route to generate all positives all of the time. This actually negates the gameplay potential of trade routes, by making it close to irrelevant which ones you choose.

Let's start with city center. In this mod, it makes every OUTGOING route cost 1 gold, and every INCOMING route generate 1food/1production. So your very first trade route between two cities with no districts will cost 1 gold for 1 food/1production - a pretty good deal.

Now lets say City A builds a Fishery. A city with a fishery will trade its extra fish for gold. So OUTGOING trade routes from that city will cost -1 food and generate +2 gold, while INCOMING trade routes will generate +2 food and cost -1 gold.

Now a trade route from City A (city center+ fishery) to City B (city center), will have the following modifiers applied: -1gold (city center A), -1food (fishery A), +2gold (fishery A), +1food(city center B), +1production (city center B), for a total of +1gold,+1production in city A.

Meanwhile, a trade route going from City B to City A will have the following, different set of modifiers: -1gold(city center B), +1food(city center A), +1production(city center A), -1gold(Fishery A), +2food (Fishery A), for a total of -2gold, +3food, +1 production.

If this all seems very complicated, here's a few rules that I hope are intuitive:

1. When a city builds a district it will attempt to trade away the goods of that district on outgoing routes. Growth districts cost food, production districts cost production. Faith, culture, and science districts all cost gold instead. Gold districts don't cost anything, and instead add a small amount of gold to trade going both ways.

2. When you send a trade route to a city, the city sending the route will receive all the goods of the city it's being sent to (and pay a price).

The logical consequence of this is that sending a route from a small city to a big city will create lots of good for the small city, at a high price in gold. While sending a route from a big city to a small city will create lots of gold from sold goods, but not generate much other yields (the small city doesn't have much to offer).