Terraforming

Terraforming changes the tile itself rather than building on it: a swamp drained into grassland, a forest cleared into fields, hills levelled, trees planted. It is paid for from the same Public Works pool as tile improvements and placed the same way, from the bottom panel onto a tile inside your borders.

• It costs far more and takes far longer than an improvement, so it is an investment: the new tile keeps paying for the rest of the game.
• Most terraforms are unlocked by a technology; Clear Improvement is known from the start and removes an improvement so something else can go there.
• A tile can hold one terraform at a time, and a wonder cannot be placed on a tile that is being terraformed.
• Terraforming a forest clears it, and clearing a forest hands the nearest city 15.