Why the map of San Francisco?

It struck me as kind of odd that there was a map of San Francisco behind Pee-Wee while he was lecturing to his friends/neighbors in his basement. Anyone have any idea why they chose SF? The rest of the movie has a pretty strong Southern California vibe, with the sunny outdoor mall and palm trees and such. As far as I know, the only part of the movie they actually shot around SF was the interior scenes at the Alamo.