Basically, every map here consists of a stack of "ground layers" (land, water, roads, forest blobs etc.) and "sprites" (individual trees, towns, mountains etc.). When the "vantage" parameters is lower than 1.0, the generator scales down the ground layers vertically, but not the sprites. It is possible to apply perspective transformation to the ground layers instead of simple scaling and make "distant" sprites smaller accordingly to create a real perspective view, but it's beyond the scope of the generator (also this).