A question that I got from my most recent game.

Got Willie randomly with a 3 seafood start. Rushed Pacal and Mutual was also a 3 seafood city with some islands visible, so I elected to go for the GLH. It was a fractal map but 7 of my 10 initial cities were coastal. I took out Ragnar with rifles/cannons and picked up 8 cities, 5 of them including the capital coastal. I didn't wan't to lose my +2 trade routes in coastal cities so I continued to Arti and was able to take one more civ (8 more coastal cities and 3 inland)

By that time everyone was defending with infantry, and I had a ton of seafood and a merchant so I wanted to found Sushi's. I teched Corp to get to AL and expected to take a hit commerce wise since the majority of my cities were coastal and hence were going to lose 1 trade route. But instead on the turn I finished Corp my coins increased. I thought, gee thats interesting, but didn't stop to investigate. Its possible that I had a city celebrating that turn and so the growth in coin, but I wondered if anyone else knew of a reason why having the GLH go obselete would result in an income increase when the majority of my population was in coastal cities.

Is there a difference in the ways trade routes from the GLH are calculated or a change in the foreign trade routes?

Corp replaces half the TRs it obsoletes in coastal cities, but it also adds a whole new one to your non-coastal cities. Since you have some non-coastal cities, and I assume both you and the AI have fairly decent sized cities by AL (10+), maybe you gained more from the +1 TR on internal cities than you lost from the coastal ones.

Remember, all cities get +1 trade route, and only coastal ones lose the trade route. So, it could be that when comparing the 5th trade route on your coastal cities vs. the 3rd one on inland cities, you got ahead.

It might be a random occurance. One of your cities grew, increasings its trade route yield (or it grew on to a gold or incense square). Maybe the different trade route yields made your governor re-arrange tiles.

I've noticed this before for me. I expect it to go down, and it ends up having practically no effect. I think unless if basically all your cities are coastal, it's not worth skipping enough.

Another possibility is an AI you had open borders with switched from Mercantilism to Free Market, that would give a big boost to trade income.

Another thing why you'll eventually need to grab Corporation is for the Corporations. Once those are pretty much available (Great Person included), then the Corporation's founding will end up being more beneficial than those 2 coastal trade routes when combined with all cities gaining 1 more trade route. But still, if you have a ton of costal cities, maximize their effectiveness as long as ya can! Tis why I find the GLH helps make 1 tile island cities actually useful.. if only for beakers and a place for my ships to stop and heal.