I found the problem with the cartographic view in v56. The "Unknown5" byte array is, in fact, an array of color data for the mini map. The map editor sets that array to all zeroes, which is why the mini map is black.
In v60 they changed the way the data is stored, so I can't just copy and paste that block from a v60 map. So, I'm now trying to figure out how the colors are stored and which colors are displayed where on the minimap. More to follow...