Boo, you got that right. The entire playable map area needs to be terraformed (I think with a tiny bit of tolerance, like 1% or so). It’s the ultimate achievement. But the areas of the terraforming buildings are really large, so it is doable. The random map is bigger than the desert valley, by the way… Also, you only need 100% terraforming, which can be achieved with 4 out of the 5 buildings.