Note: This page is taken from n.wikia.com.
An Incomplete map is a half-finished map. Maybe the author made an adequate tileset, but was not sure where to put the objects; or perhaps they started a map but did not have the time to finish it. The level data is often used by others to make a complete map. If one finishes an incomplete map, they should make sure to acknowledge the original author!
This map category is quite often seen in nv2 in form of a tileset map, unlike in form of tileset + objects.