At first glance this seems really easy. Just look in Simulation/SimulationDescriptors[TerrainTag] or Simulation/SimulationDescriptors[TerrainType], and change the yields in there. Simple, right? Not so fast. This will change the overall yields, but there's a problem. Let's say you open TerrainTag and change the entry for forests (which gives all forest terrain +1 Industry) from this:















To this:



















You've just added one science point per forest, right? Test the mod, and you will see that forests indeed are now giving science as well as industry (even ones that didn't before). But test it on the Vaulters (with the knack for knowledge trait giving +1 science on any terrain with science), and there's a problem. The Vaulter's aren't getting the knack for knowledge trait on the forests that weren't getting science without the mod. So say on a temperate forest (normally +1 food, and +1 industry), you would be getting 1 food, 1 industry, and 1 science, instead of the 2 science you should be getting with the trait (This is bad as all of the city improvements that give +science on any tile with science won't work either). What's going on here? That took me a good bit of digging, but I finally cracked it.



In the mapping folder is a large file called TerrainTypeMapping[Terrain]. This contains a list of every terrain type in the game. Under each terrain type is a layer for simulation, which has different terrain tags for that type. So if you wanted to add science to forests, just search for terraintagforest in that mapping file, and add a line for science for any forest that doesn't already have it. This way everything will know forests have science, and all the abilities that rely on a type of terrain having a particular yield type will work correctly. Of course this applies to any type of terrain and any type of yield. If you want something that doesn't normally give a certain FIDS that FIDS, you have to change the mapping file for each terrain type your changing.



Hope this helps someone.