Echohawk
Shirokinukatsukami fan
That article is by Gary Gygax, and seems to be him thinking out loud about how planes should work in D&D. There is an early version of the great rectangle diagram from the PH, but it also has all the inner planes squished inside it like a flattened donut (and no sign of the Outlands). The bulk of the article deals with how magical weapons might function across the planes. There's nothing much there about how Gary decided on which planes, or how many there should be. All the planes are listed in the key to the diagram, and there is a note there about how it is possible to walk between adjacent planes.(Un)Reason's Dragon Magazine thread mentions an article from the July 1977 issue (Dragon #8) as containing "the first proper map of the planar cosmology." He doesn't mention who wrote it or go into too much detail about the contents.