There’s an interesting discussion underway about whether rising population necessarily leads to rising land prices over time. Bill McBride of Calculated Risk says yes:

A key reason for the upward slope in real house prices is because some areas are land constrained, and with an increasing population, the value of land increases faster than inflation.

Noah Smith disagrees, because land isn’t really particularly scarce — when we see high land prices in some metro areas, it’s all about the agglomeration effects, which could go in various directions over time.

My first reaction to Smith’s comment was that it might not matter very much, because new metropolitan areas are very hard to create; there may be plenty of land around Lubbock, but nobody’s going to move there, so a growing population has to squeeze into the metropolitan areas we have. But then I realized that this might not be the last word either; even if people want to stay in existing metro areas, they can hive off “edge cities” at the, um, edges of these metro areas, so that the relevant population density — the density that makes land in or near urban hubs expensive — might not rise even if the overall population of the metro area goes up.

And we have data! Via Richard Florida, new work by the Census (pdf) calculates “population-weighted density” — a weighted average of density across census tracts, where the tracts are weighted not by land area but by population; this gives a much better idea of how the average person lives.

As Florida points out, the new measure conveys a much better sense of how metros differ. For example, by the standard density measure Los Angeles is actually denser than New York, basically because LA is hemmed in by mountains, limiting how far the sprawl/commuting zone can reach. But New York has an urban core in a way that LA does not, and sure enough, it has a much, much higher population-weighted density.

What I wanted, however, was trends — and the Census has calculated this measure both for metros and for national aggregates for both 2000 and 2010. Here’s what it looks like:

Photo

So, a couple of points. First, although America is a vast, thinly populated country, with fewer than 90 people per square mile, the average American lives in a quite densely populated neighborhood, with more than 5000 people per square mile. The next time someone talks about small towns as the “real America”, bear in mind that the real real America — the America in which most Americans live — looks more or less like metropolitan Baltimore.

Second, however, although the US population and hence the population density rose about 10 percent over the course of the naughties, the average American was living in a somewhat less dense neighborhood in 2010 than in 2000, as population spread out within metropolitan areas. If you like, we’re becoming a bit less a nation of Bostons and a bit more a nation of Houstons.

This is, I think, a picture of urban geography in which the link between overall rising population and land prices is likely to be diffuse at best. So I think I call this one for Smith — although McBride’s point that actual real housing prices do seem to have an upward trend remains important, and needs explaining.