Cities Skylines pollution filter?

Hey all,
I would like to discuss over the best method or options to accomplish what Cities Skylines did with their traffic, pollution, and resource filters. I'd like to have a way to show areas of the terrain as a color indicating it's status in relation with...whatever. For example, if there is a heavy concentration of enemy presence in an area of the map, I'd like to have a red blob in the area. I thought maybe projectors, splatmaps, or shaders or even some kind of combination. I really have no clue what direction I should head in. Thanks!

 

I haven't tried yet and can't say if it's best solution but I found the link http://www.alanzucconi.com/2016/01/27/arrays-shaders-heatmaps-in-unity3d/ several days ago
It could be a good start

 

At first glance, I believe this is exactly what I'm looking for. Thanks so much!