Terrain is a major part of the game. It is not longer just "water" or "elevation". Instead different terrain types will directly impact movement speeds, detection, and even weapon damage.
If you hover your mouse over an area you will see the terrain type listed. Thicker terrain offers more concealment for ground units and facilities than an open plain.
The Land Cover map overlay gives a full color detail of different terrain types. The above example shows red as urban, light yellow as cropland and brown as grasslands.