Here is another quote from Gygax on the nature of Oerth in particular the nature of the Greyhawk maps from POLYHEDRON #12 (JUN 1983):
The Greyhawk game campaign Setting was designed with only broad details in order to facilitate the bullseye method of milieu design and development. It does not provide much for detailing relatively small areas of the campaign. In this regard, collections of ready-made fortresses, castles, villages, and cities are most useful. (l am still trying to get TSR to produce some superior material in this regard.)