Okay, one more question. If the tile has no improvement but it does have a not-all-bad feature (Forest), should I show it as improvable if the best build is an improvement that removes it, say a Mine or Cottage? Right now I only show it as improvable if the feature is only bad. Hmm, no that won't work. This will block Plantations on Silk in a Forest. How about making an exception if the improvement unlocks the bonus on the tile; that should probably flow through first in all cases. Show as improvable if the build will provide access to a resource, increase a tile yield without losing a good feature or other improvement, or remove a bad feature. This is like a game of whack-a-mole!