I tried to search for the answer to this question but came up empty... so I apologize if this has been asked before. How come I can't get a worker to "improve" a tile, say grassland, to a pasture, mine, camp, etc (after I've researched it)? I click on the action panel and it just has the basics. According to the manual you can upgrade about any type of tile-- as long as it doesn't contain a resource. The AI doesn't seem to care-- they can build just about anything but for some reason I'm not getting the "advanced" improvement options. What am I missing?