Personally , I would say they work with an RGB split node, to perhaps assign different materials to each area of the map that is red, green or blue, and maybe the black is used with an alpha to make that area transparent? So in the example of the second image, maybe the black area is ocean , so it has to be transparent for a shader for water to work, and then the red, blue and green are an island with seperate materials assigned by the RGB split node for beach, trees and mountains? Something along those lines anyways. It just looks to me like an island from above and ive used similar maps with RGB split to assign different materials to the R G and B . A bit like an ID map…..
