In Green Hill Zone, anything black absolutely *cannot* be reached in any way. Extracting the maps from the game shows there is some data there, but showing it would result in spikes floating in mid-air for example so I don't show it and stick to a 'visible in-game only" template. In Marble Zone, you can go everywhere in Debug Mode but the black sections are all empty and unreachable by normal means anyway while playing so I don't consider them as part of the map. I *could* fill this void with either lava or bricks but since there's nothing there and I don't like to add stuff that's not there, I prefer to keep it black.