If my platoon is taking a Sunday stroll over wide open fields so that if I stand on top of my buddy's shoulders I can see 10 mile in any direction... or a dust cloud from an enemy mobile division rising 15 miles over the horizon... I could literally see farther than my weapon could fire.

On the other hand... that same stroll through the wooded forests of Germany, or the winding roads through the Alps, I wouldn't know what's on the other side of the outcropping until I got there and took a look.

Proposal
The Fog of war in Enemy territory should be Terrain Dependent. Longest over Water and Plains (100%), decreasing as you move into Hills (80%), then shortest in Forest and Mountain territories (50%). Units with Scout ability increase that range( +50%)

Airplanes should be able to see farther (even though they can't ID the units within an army). Right now they only see what they can attack in their Blue Dot. One would think that with that higher vantage point, they'd be able to spot dust plumes in the dessert a lot farther away than a guy on the ground, or ships at sea would be visible from a much greater range than what you'd see from a crow's nest.

Each unit already tracks it's location... as to which province it is in. Armour gets bonuses to combat stats in plains and penalties in cities (to HP and combat Stats)..

All the different provinces are Already coded for terrain type.

Wouldn't take much to add a multiplier to Sight range by checking location of unit, and unit with best range gets the job in stacks.