SetUnknownRegions: This command declares the regions which are not known to civilized nations (ie uncharted / Terra incognita). All the rest wil be known when this command is called.
eg SetUnknownRegions = $NorthPole|$SouthPole
Will make these 2 uncharted and the rest of the world explored.
SetKnownRegions work a bit in reverse, ie it allows to add one (or several) regions to the explored list.
Uncharted regions appears with a generic texture and without any information about them. Only leaders with Explorer ability can penetrate them (with some men).
note: This only work for VGN (ie if RuleExploration is Simple or above).
note2: with RuleExploration Advanced, each faction maintains a list of known regions (no game use that for now).