As far as the city section goes, fantasy-maps.com has some rather nice free tutorials on drawing isometrically here :http://fantasy-maps.com/tutorials/. Perhaps you could apply the techniques he suggests to a much larger area of the map? You could even create a lot of different brushes of the same size, and use Rob A's random density maps with the appropriate settings (http://www.cartographersguild.com/sh...5584#post25584) to create a large non-repeating fill. You'd have to break up the edges afterwards to keep them from looking too blocky, but it'd be a lot easier than trying to draw the whole thing out by hand. As far as the chemical areas, I'd try some sort of clouds texture, but I'm much less sure there.