I was exploring a bit with my Sovereign when it hit me. The game has different ranges of sight, but no concept of Line of Sight (LoS) yet.
I wandered inside a valley in the mountains, not able to climb them (great mountain design btw. ) but somehow was able to see through those mountains to the other side. That shouldn't happen I think.
Also forests should also block line of sight imho, just to a lesser extent I guess. You can see one square deep in to forest while mountains block LoS completely. (You should be able to see the mountains themselves still, or we would end up with black spots on the map which can't be explored. And I'd think that would be annoying. Just no looking behind mountains themselves.