A few more possible inconsistencies regarding "base terrain" and "terrain features." Not sure if this is intended behavior or not. Maybe +1 commerce next to river is only true if there is no feature, or if the feature itself indicates +1 commerce next to river? But just to make sure below are the scenarios:
1) Marsh terrain with no feature on it next to river gives +1 commerce, +1 food, +1 hammer as the civopedia says it should. This is good.
2) Marsh terrain with tall grass feature on it next to river gives +2 food, +1 hammer but does not give the +1 commerce that the base marsh terrain would get. It does add the +1 food correctly though but nothing in the civopedia says that it should subtract the +1 commerce that the marsh terrain gets.
3) Marsh terrain with swamp feature on it next to river gives +1 commerce, +1 hammer. It correctly subtracts a food, but it should also add another +1 commerce due to swamp next to river according to civopedia. Both the base marsh terrain and the swamp feature are suppose to add a +1 commerce next to river according to civopedia
I did not test for all features on terrain, but I have a feeling other "base terrain" and "terrain feature" combinations are being calculated similarly...
Also, I noticed that "hills" are not described in the civopedia at all?
EDIT: I guess this is all intended behavior after all, following the original Civ4 behavior when forest feature is adjacent to river. My only comment on this then would be that as more and more possible features are added that the "next to river" consideration is made for it if it makes sense, and it looks like this was done for many of them hence some features also including the +1 commerce next to river attribute. However I'm wondering if it makes sense that a tall grass feature would remove this +1 commerce? I forget the rationale why forest removed it to be honest...