It's amusing that Ben Franklin's advice to buy land was made at a time when the U.S. was approximately one tenth its current size. While this country does not have the stupefying vastness of Siberia, our acreage makes for a wide range of decisions when it comes to settlement patterns. We have tended to settle in flatlands; near water, usually in floodplains, and have resisted frontier building when the opportunity to do infill has presented itself. This trend has persisted into modern times. The word "sprawl" conveys an image of lateral growth in all directions, but developers have focused their efforts on clustering homes and strip malls along transportation routes. The strands in the net get thicker, but the spaces between the strands stay empty, and in some areas, they empty out even more.
Increased energy costs will make some of these settlements harder to sustain than others. Manhattan is held as a paragon of green, high density development, while the Broadacre City envisioned by Wright is a dangerous fantasy. The truth, and the eventual future outcome, will be somewhere in between. I don't predict a resurgence of decaying small cities in the Northeast unless climate change makes the agricultural picture more robust. Las Vegas is toast, Detroit is doomed, and Miami is the next Atlantis. Atlanta may be a surprising utopia, but not for a hundred years.