If I remember correctly there is a good blurb about this in Everybody Loves A History - Graham flying across the US and marveling at the expanse, or something along those lines. Flying across the US starts to get a little odd because of all the farms - enormous grids and circles from the irrigation systems, and they just seem to go on forever. Might be the best way to experience America.
Depending on how you look at it this coordinate might describe the "center of America" - though just as with statistics, it all depends how you juggle the numbers and/or rules for figuring it out. It is generally agreed the geographical center is actually a bit to the northwest in Lebanon, Kansas, though Graham's Map Ref. is very, very close to Centerville, Iowa - which doesn't really hold much of a claim to the title. (I think Graham mentioned this town in a separate discussion of Map Ref.)
The inspiration for the first part of the text was my first daylight flight across the USA from West to East in the summer of 1978... across the Rockies and the vast Mid West... somewhere close to Centreville seemed to be the perfect notional place after which to title the song. The second part of the text was written from an earthbound perspective traveling by road through the Lowlands of Europe... the greenhouse agriculture of Holland... crystal palaces for floral kings etc....