Currently the terrain spread by empire and kingdom zone of control is almost purely cosmetic. I believe there are some combat adjustments (small bonus/penalty) but that's about it. I have an idea to expand on the system to make it and the resource system a little more interesting.
As is resources exist on the map no matter what sort of terrain surrounds them, fertile land is apparently fertile even in deserts and wastelands, and the only way to claim them is to expand your ZoC over them. What if the terrain controlled which type of resource a node provides (if any)? Say in a desert a node is represented by dead plants, and by altering the land it becomes a random food resource specific to that terrain type. If revived by a kingdom or spell maybe it turns into wheat or an orchard, by empire maybe it becomes a new resource that makes more sense like a fungus field. Further what if a node doesn't have to be in your ZoC to claim, but only has to be unclaimed and on the correct terrain type? So you see a node a few tiles outside of your ZoC, now you have three options, wait a bunch of turns for your ZoC to expand, build a new city near it, or send a channeler to terraform the land and claim the node. Claimed nodes outside your ZoC would not be attributed to a city, so you couldn't boost the resource with appropriate buildings. Nodes inside your ZoC would be locked and unclaimable by other players, however an enemy spell caster could cast a terraform spell and make the node unusable until it returns to the correct terrain type, either naturally after a bunch of turns or by casting the correct spell to fix it.
Resources like metal or gold are harder to adjust, but what if you don't know what type of node it is until terraformed? So you just see some sort of ore deposit, and it's not until you send a caster to terraform it that you know what it is. Let's say it's harder to dig a sample tunnel to check the ore underground when the surface is all sand. I think that would add another level to exploration.
I think this would spark a little more competition over resources, especially those lone nodes out in the middle of nowhere that nobody wants to build a city near, and also make the terraforming aspect of the game much more interesting. It could also open the way to further expansion on the terraforming concept, like a faction that spreads and controls snow/ice terrain, or other new terrain types like swamps or some sort of fiery magma hellfire terrain.
