More than 77 million people live in the Southeast, a part of the United States that began to grow rapidly in the latter half of the 20th century, thanks in no small part of the rise of air conditioning and automobiles (and some of the trends we discussed here).

Development there looks notably different from urbanized parts of the Northeast that were built in a very different era (think Boston, Philadelphia). Southern cities and their suburbs tend to be lower-density and car-dependent, with more large-lot, single-family homes. Communities often leap-frog across the countryside, creating a kind of patchwork development that consumes a lot of land. And amid all of these patterns, the region's rate of population growth over the last six decades has been about 40 percent greater than the rest of the country.