The Overhead Wire asks what sprawl is. Ryan Avent gives his answer -- he uses "sprawl" to refer to neighborhood density rather than regional density. (As a stats geek, I would state it this way: "What matters is a metropolitan area's weighted density and not its standard density.")
My own thought it that it's time to retire "sprawl." This
little 5-letter word is being forced to do too much work; it simply has too many meanings. And it might as well be a 4-letter word because it is the land-use equivalent of "asshole" -- I've told you I don't like you but I won't bother getting specific.
Here are different meanings I've seen it given: (1) peripheral development -- greenfield development at the fringe of an urban area (one variation singles out "leapfrog" development); (2) economic dispersal -- the rising cost (in both time and money) of getting from point A to point B; (3) "pod" development -- any development sharply segregating single-family, multi-family and commercial uses; (4) low-density development -- always a relative metric, of course; and (5) auto-dependent development. I'm sure there are others.
"Sprawl" literally means "to spread or develop irregularly." That best matches (1). But what makes it such a slippery word is the correlation between these definitions, which causes people to conflate one meaning with another. Peripheral growth can lengthen commutes. Virtually all new suburban development is "pod" development, and low-density development at that. And everything built more than a quarter-mile from a rail station -- virtually any suburban development -- is car-dependent, or at least car-oriented. It is therefore unsurprising that people use "sprawl" to encompass several meanings at once.
For example, Dolores Hayden in A Field Guide to Sprawl defines "sprawl" as "a process of large-scale real estate development resulting in low-density, scattered, discontinuous car-dependent construction, usually on the periphery of declining older suburbs and shrinking city centers." So she combines (1), (4) and (5), and possibly (3) as well, and throws in a jab at tract development for good measure. (Note, though, that combining meanings technically narrows the definition rather than expands it.) There are many others, of course.
But it's sloppy to mix them up. The correlation is imperfect. New Urbanist developments that mix single-family, multi-family and commercial uses into a walkable neighborhood are often built on greenfields at the periphery of urban areas and are not served by transit. Density is not a perfect proxy for urban form because pod developments are sometimes denser than traditional, walkable neighborhoods; this is one reason why places like Phoenix have a relatively high weighted density. Infill development is frequently not served by transit and consists of segregated uses. Commuting costs can rise with rising density as well as increasing geographic dispersal if the transportation infrastructure is not up to snuff.
Each of these definitions suggests a different problem. You cannot propose a solution until you have told the rest of us what problem you are trying to solve. And "sprawl" is simply too mushy to do that. If you are worried about the loss of open space, then New Urbanist greenfield development must be included within the definition of "sprawl." If you are worried about rising commuting costs, it makes no sense to include greenfield development served by mass transit. If you care about urban form -- if you hate pod development, for example -- you should include pod development whether it's core or suburban, dense or sparse. We're engaged in lots of different debates over land use but we often don't realize it because we use just one word to characterize them all.
We need to develop more precise, clinical terms to advance the discussion. Medicine, math and science (and law, more or less) define their terms precisely. People make fun of jargon, but serious disciplines need it to keep distinct ideas straight. As used today, "sprawl" is the medical equivalent of "sick." Imagine the hilarity that would ensue if doctors used "sick" as their primary term for both prostate cancer and the flu.
Define terms precisely. And don't build moral judgments into them. You can cast aspersions once everyone else knows what you're talking about.