I was reading the thread about not using the north up assumption and it occurred to me that it might be on the way to a good idea for a challenge idea. But why stop there? Not only does north not need to be up, but there need not be a north at all. I propose a challenge wherein your map must use an alternate coordinate system that can't just be a renaming or reorientation of the four point system. Not only does it need to be plotted as such, but the labels need to be reflective of they system to carry the theme through. Fun or too open ended?