Any country has three sources of Intelligence: Ground Reconnaissance, Signal Intercepts, and Spies.

Ground-based reconnaissance involves only what can be seen from the ground, and is represented on the map as “fog of war” (i.e. areas you can’t see). You can also fly over enemy territory (during wartime) and see what’s in a province.

Radar stations are not just for “radar,” as they also act as Signals Intercept (SigInt) stations. They have a limited range for radar and signal intercepts, but a further reach than simple observation. Radar stations can be improved with technology advancements, and by improving the level of the radar station (i.e. building another level). Higher-level stations can see and detect further from the point of observation.

You can deploy spies to other countries, and set them to look for certain types of information. You can also give them “covert action” missions, which may undermine the government, or sabotage production, etc. You can set spies to operate in your own country, either to catch enemy spies, or to manipulate your population (making them more supportive of your government, or more willing to go to war, for instance).