There is another map that was posted recently with the same issue. I explained in that thread... can't seem to find it right now. Anyway, it has to do with the lighter colored floor and darker surroundings. We have been trained from early age to equate lighter with higher - consider a standard map that has the white peaks denoting highest elevation as well as the water color darker is deeper. So when you are presented with a map like this regardless of the bevel we immediately process the lighter color as higher. The shadows simply magnify the effect and make it more pronounced.