This is the original artwork for all three of the Planetary Maps.  It looks like either acrylic or oil on gessoboard, and depicts a minor battle on Endor.  This artwork was used for the back of the Planetary Map, and is pretty much obscured by product information and pictures, a grid like pattern, and a whole side dedicated to the Planetary Map, such as Endor, Death Stars, and Tatooine.  However, looking at this piece up close really shows the amount of detail used, even for something that could be considered a throwaway.

You can click the below images for more close ups of the artwork itself.