Not strictly map related, but I was stunned to learn that the Nonprofit Internet Archive has made scanned copies available in a variety of formats of most of Dragon magazine and Polyhedron magazine. Although there are hundreds of maps scattered across the issues, the shear wealth of advice, background articles, support articles and general ideas available for rpgs in them is hard to describe. Dragon magazine can be found at Internet Archive Search: collection:dragon_magazine and Polyhedron magazine can be found at Internet Archive Search: collection:polyhedronnewszine