When I try to export a .gmap from the terrain editor it doesn't seem to put the proper terrain height information into the various .nw files.
For the most part the .nw's vaguely resemble the .gmap. If there was a big enough mountain for example... then it appears in the graal editor.
However shorelines are misplaced, islands are misplaced or missing or blown up into peninsulas. There are black fractures inbetween many of the .nw borders and in some .nw it didn't even save any terrain detail at all. It's just a big giant dark blue hole filled with water that cuts through whatever is around it.