it's a bit more complicated than that but here are a few:
(t = temperature, h = humidity)
t: 0 - 25 & h: 20 - 50 = grass (with enough trees it's forest)
t: 0 - 25 & h: 0 - 20 = wasteland
t: 0 - 25 & h: 50 - 100 = swamp
t: 25 - 40 & h: 40 - 100 = tropic
t: 40> = desert
t: 30> & h: <40 = desert
t: 25> & h: <10 = desert
t: <0 & h: <30 = tundra
t: <0 & h: 30> = snowfields
tiles can be flagged with a *special* number resulting in mountainous/oil/volcano/town/city
sea and deep sea tiles are locked unless a meteor changes it