Welcome to CFC, nbd! There are actually 3 main terrain resources in C3C, too: food, shields, and gold. Not every tile produces all three, though. for example, an unimproved grassland tile, if not on a river, produces 2 food. Add a road and it will produce 2 food and 1 gold. If you then add a mine, it will produce 2 food, 1 gold, and 1 shield. (Or have I totally misunderstood your question?)