Lady of Fortune Caelum

Maybe it's not clear.

In the Nation Selection in the Flavor Text it will say your Nation/Theme's Temperature Preference. If a province is not that Temperature (either Cold or Heat) then you have a Economic and Supply penalty.

-5% Income, -10% Supply.

So if you look at Caelum, it has a Cold 3 Preference. That means in anything but Cold 3 enviroment they lose money and supply. So Normal Temperature they are at -15% Gold, -30% Supply. Heat 3, -30% Gold, -60% Supply.

Supply is based off of Province Population (do a search for exact #'s) and Supply Usage is calculated by Number of Units and Size of Units.

Did that clear up any confusion?