(Presuming you mean something like
this (almost maybe spoilery) map from WaDF.)
I cant imagine how one could make a new level without such a tool.
The way all levels so far have been made. The nearest was this thing posted on the old forum that put a BMP file of each screen of a level in one folder.
While something like this would be really neat, I don't know how practical it would be. The really big levels can have more than 1,000 screens, and any view of it would either be so zoomed-out it would be useless, or incredibly memory-intensive in its sheer size and detail.
Also, many levels are not entirely linear: there are shifts and warps linking disparate locations. A map of a boss battle, for example, would be useless, as it'd just show a long line of near-identical screens.
I'm pretty sure that most of the maps in the archive (like the one linked to above) were made using the source of the game. Before very recently, KS was closed-source, so this sort of thing couldn't be done. Even now, it might be unworkable because none of the levels or tilesets or gradients are actually built in to KS.