Probably a little of both - playability (so you can plan operations), and abstracting intelligence that isn't represented in the game. Photos from sub recon missions, radio traffic, etc.
I agree, I also think of this as the work of spies, military attaches and other HUMINT. After all, it may be easy for troops to hide, but building a dock or a runway is a pretty permanent addition, and would be obvious even to casual civilian observers.
Playing/Learning Shadow Empire