Comments on: Why America’s population density is falling A slice of lime in the soda Sun, 26 Oct 2014 19:05:02 +0000 hourly 1 By: Ralphooo Mon, 20 May 2013 20:57:08 +0000 Numerical measurements are bound to seem paradoxical if they are misnamed. “Population-weighted population density” is no doubt a useful statistic, but it is not a population density in the ordinary sense. This measure could very well be called the “crowding index.”

To illustrate this, consider a sparsely-populated rural region that has only one big shopping mall. During the day, some of the regional residents work in the mall, and many others shop there. People living outside the region seldom either shop or work there.

The result? During working hours, the “population-weighted population density” of the entire region shoots far above its value when the mall is closed.

You might say the whole region becomes more crowded Monday through Friday, but I, for one, would not like to say it becomes more dense.

By: Memph Sun, 12 May 2013 18:10:38 +0000 @LetsGoLA, that’s only an issue with cities with large dense cores though. Calgary grew in the way you described, with all parts of the metro getting denser but most growth occuring in the suburbs, however, outside the downtown, the core is no denser than the suburbs, so the weighted density increased significantly. The same could have happened in many sunbelt cities but it seems most have larger areas of the core that experienced significant population loss and lower density and more leapfrog suburban growth.

In addition to the fact that a larger share of growth occured in lower density metros and lower density parts of metros (outer suburbs), there is another factor: post123.html

By: TGraham Sun, 12 May 2013 05:41:48 +0000 We can find abundant examples of where density is rising (that’s what apt and condo development does)… and also where low-density sprawl continues.
In most major metros you’ll find both these dynamics. Which is the more prominent — affecting a larger population — determines whether a given metro’s “population-weighted density” is ebbing or growing.

But recognizing coincident contra-trends does not seem to be the point of this blog piece. The author seems more interested in pushing a storyline about inner-city gentrification.

Finally, I’m not impressed by the glossed-over assertion that “population-weighted density” is the one “right way” to discuss land use. I much prefer our usual approach: We clip the urbanized area; then calculate land-weighted density within the urbanized area. If someone thinks “population-weighted density” is preferable, that needs to be explained.

By: LetsGoLA Mon, 06 May 2013 20:14:12 +0000 Nope. Felix and Krugman are both making the same error regarding weighted density. If the rich people condo anecdote were true, that would make actual population density fall in addition to weighted population density. High rise residential development in the US, with the exception of Manhattan, is basically irrelevant to population density trends. What’s happening is that low-density areas are adding population faster than high-density areas.

Consider a metro with three areas: a 100 sq mile core with 500,000 people, 300 sq miles of old suburbs with 900,000 people, and 1000 sq miles of sprawlsville with 1,000,000 people. Density is 1714/sm and weighted density is 2583/sm.

By the next census, the core has increased to 101 sq mile (because zoning/permitting makes it hard to expand) and 515,100 people. The old suburbs have increased to 315 sq miles and 976,500 people. Sprawlsville has increased to 1200 sq miles and 1,260,000 people. Density is 1965/sm and weighted density is 2536/sm.

Note that every zone (core, suburb, sprawlsville) got denser and overall city density went up, but weighted density still went down.

By: EliRabett1 Mon, 06 May 2013 15:29:13 +0000 Well sort of. Urban core densities have been falling since at least 1920. Back to the 1800s for Paris and London, for pretty much the same reasons you put.

By: realist50 Mon, 06 May 2013 00:45:12 +0000 +1 to Nameless, and I think that Felix misses the point that a decrease in population-weighted density need not mean that density declines in any particular neighborhood. It can occur simply because population grows faster in less dense metros and neighborhoods.

By: Nameless Sun, 05 May 2013 20:50:54 +0000 It’s interesting to look at the raw numbers to figure out what exactly is going on: iles/CBSA%20Report%20Chapter%203%20Data. xls

First of all, metropolitan area population weighted density is in fact down 6% in 10 years.

Next, a mathematical curiosity. Population weighted densities of the two densest metros (New York and Los Angeles) are down 1.4% and 2.6%. Population weighted density of all other metros combined is down 4.9%. So how is it possible that the density of all of them together is down 6%? The answer is that NY and LA have been growing slower than the rest of the country – their populations grew only 3-4%, and the total population of all other metros grew 12%. When low density metros grow faster than high density metros, overall density goes down. It’s a form of Simpson’s paradox.

Once we exclude NY and LA, the rest of the list is pretty noisy, but one can discern two groups. In MSA’s with initial weighted population densities above 1200 people per square mile, median density change is -3.5% (with no apparent trend). In MSA’s below 1200 people per square mile, median density change is +0.8%. Census has a very broad definition of “MSA” (metropolitan statistical area), which, for example, includes Glens Falls, NY (population 129K). Among “real” MSA’s (populations of 1 million or more), median density change is -3.6%, again with no apparent trend.

By: Nameless Sun, 05 May 2013 19:50:55 +0000 I’m not sure if effects described by Felix are real (at least where he lives). Census reports that the population within 2 miles of New York City Hall increased by 9.3% between 2010 and 2010.

There is also at least one effect that is likely stronger than those described above. What did happen, really, between 2000 and 2010? We had a housing bubble, and it led to a construction boom. Some of it took place in city cores, but we saw significant growth of suburbs and exurbs, built out with low density housing. As suburbs grew, they soaked up population growth and attracted some people to move from city cores into suburbs.

According to the census bureau, between 2000 and 2010, the number of apartments in massively multi-unit structures (50 or more units per building, city core style) increased by 5%, from 6.13 million to 6.47 million.

At the same time, the number of single-family detached houses in the country increased by 16%, from 69.9 to 81.1 million.

By: KenG_CA Sun, 05 May 2013 05:13:11 +0000 Or maybe it’s just sprawl? If the metro areas get larger, but the population doesn’t increase in the expanded areas with the same density as the core, the density of the metro area will decrease. I think that will have a bigger impact on density than foreigners buying homes they rarely spend time in.

By: ErikKengaard Sun, 05 May 2013 02:02:47 +0000 What nonsense. Time series data for desirable urban/suburban areas (that would exclude Detroit) shows a relentless increase in density over the past 70 years. 11
housing units per square mile in 1940; 36 in 2010.