Slightly related, I
dumped Utopia (another isometric game) a few years ago. Never occurred to me to also dump the game maps and plot in ore/fuel deposits. Perhaps I should do that.
I generally prefer to dump (reverse engineer the gfx routines) over ripping (taking screenshots). In some cases that's not easily done though, Exile's map and Solar Jetman's sprites for example.
In Utopia the gfx were bitplaned, each with a different height but constant width. The heights were stored in a table. Since the game doesn't load during map scrolling and there's some complex design going on, I figure the map data must be pretty much uncompressed, probably a simple array. It's possible that they used bits of a byte as flags or something. Stuff like that is tricky to figure out.
Once you have the gfx and map data, writing a thing which draws the map is almost trivial. Of course, if you got that far you can also edit the gfx and map in the game.
With older games like in your example (actually, 1991, that's the same as Utopia), chances are that they had to use tricks to make things fit into memory and if that's the case, dumping is much harder. The iso map uses height in a way that Utopia doesn't.
I prefer seeing plain colors on maps like these, but graying a few colors to use as bridges (or just plain saturation contrast) might be a good idea. I'd definitely desat one of the grass greens. Helm pretty much did what I wanted to do, pulled in some desat blue in the darker green, warmed up the lit green. I see a problem with the grays though: in one case a light gray is a shadow, and in another it's the lit side. This creates an inconsistent feel if you're going for a consistent cold-warm ramp (roads/mountains feel cold). It might be possible to keep the light gray
relatively cold instead, by warming up the white (but I'm not sure if you can afford not having a neutral white).
The chaotic dithering in the water is something I'd change.
