I mostly improve existing and add historical maps to Wikipedia articles.
Many of the historical maps I've seen on Wikipedia are pretty lackluster. In my opinion historical maps should be more than just a colored blob on a land background. They should give the viewer a sense of what cities, settlements and rivers used to be important back then. They should be high quality, easy to read and be in a projection that makes sense. I try to cite the sources of every map in their respective Wikimedia page.