In-game maps are almost always functional and that's it. I much prefer a screenshot maps or, in the case of 3D games, a map made from polygons and textures that really show the beauty of the game in action.
Unfortunately, it's not always possible to do that, especially with those old pseudo-3D games where you don't even have actual textures and polygons to work with.
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Current projects: Bucky O'Hare (NES), Metal Storm (NES), Clock Tower (SNES), Ristar-The Shooting Star (Gen), Sonic The Hedgehog (Gen), Sonic CD (Sega CD), Mega Man Zero (GBA), Battletoads (NES)