- Artillery should not act as a radar. I get it. It's cool to see the impact, but it utterly destroys the purpose of radar altogether. Perhaps if it's not too difficult, the impact area could be temporarily revealed a few seconds before and after, and then return to blackness.
- Artillery should not auto-fire at enemies that haven't been detected by radar. This improves the necessity for radar as it is, and even more so as I suggest below, as your artillery will rely on the detection before it can even fire. Of course, manual firing can still be a thing.
- Monitoring: The current radar, minus the expanded scanning mechanic. A radar with only monitoring capability would only actively reveal a small area.
- Deposits: A radar with deposit scanning would scan a wide area for iron, copper, coal, stone, oil, and uranium without revealing anything else about the map.
- Enemy Building: A radar with enemy building scanning would scan a wide area for enemy buildings, and reveal them without also revealing anything else.
- Enemy Unit: A radar with enemy unit tracking would actively track units within a wide-but-smaller area. Useful for advance warning of attacks. As a side note, a building with this sort of tracking could theoretically include alarm functionality.
- Topology: Topology scanning radars would reveal the actual map itself. As this information is useful, but less so than the others, it could be relatively cheap.
Either the radar types could be implemented as separate buildings, or as modules (similar to speed, efficiency, etc.) to be added to a base building. Separate buildings is acceptable because current radars have a somewhat large placement area within which the scanning area is considered the same.
Each scanning type could be a separate inital tech, with infinite range techs later. Monitoring would likely be the cheapest/first tech, with topology next, followed by a branch for enemy building and deposit, and finally by enemy unit.
Perhaps adding a radar car might be worth looking into. Keeping visibility on trains and their paths may be useful. I've honestly not thought much into this.
- Stationary/wagon missile launchers. Meduim-long range turrets best used with explosive rockets to take out or weaken groups of enemy units.
- Make missile launchers more useful by occasional combined attacks with VERY large groups of enemies.
- These two combined give a lot of use into the enemy unit radar type.