Austin Contrarian

Prop 3 voting results

Ryan Robinson, the City's demographer, has put together this map showing where Proposition 3 (10-1 representation) received its votes:

I don't think there's any surprise here. Suburbanites -- and even central voters south of Lady Birdy Lake -- concluded that they're not well represented by the central-Austin-dominated Council.  

10-1 did poorly in west Austin and the central neighborhoods north of UT. A cynic might claim that these voters opposed 10-1 because it will dilute their outsized influence on City Council. I'm an optimist, though. I'm confident all those Tarrytown and Hyde Park "nay" votes were spurred by the fear that 10-1 will lead to ward politics and more NIMBYism.

78704 really is losing children

Stephanie Myers last week had a piece in the Austin Post entitled, “Are Families with Children Being Forced Out of the City?” “Forced” is a loaded term, but families with children undeniably are a declining share of central Austin’s population. Families with children have been declining in share for decades and, as Myers notes, are now declining in absolute numbers in the central city as well.

Why this is happening is up for debate. A fruitful debate, though, requires accurate facts, and I think it’s important to correct the article’s impression that the 78704 zip code somehow is “bucking this trend” and seeing a rise in children. (To orient the out-of-town readers, 78704 is the zip code directly south of downtown Austin.)

The Census data show, clearly and unambiguously, that the population of children in 78704 declined between 2000 and 2010. Back in March 2011, I ran a table showing that nine of the eleven census tracts in ’04 lost children, and the zip code lost nearly 1,400 children overall.

A few months later, I published this chart showing that the population in the zip code declined for every single year of age between birth and seventeen.

 

The loss of children was broad and deep.

There’s yet another way to measure the change, and that is relative to the Austin average. Divide a census tract’s percentage of population under 18 by the citywide percentage of population under 18. This number (itself a percentage) tells you the concentration of children in the tract relative to the citywide average. This is sometimes referred to as a “location quotient.” (The Census Bureau used location quotients extensively in its recent report on U.S. metro area.)

For example, in 2010, 11.15% of the residents of census tract 13.03 (Zilker) were under 18 while 22.2% of all Austin residents were under 18. Children thus were concentrated in tract 13.03 at just 50.2% of the citywide average concentration.

I calculated the location quotients for children under 18 for all of the the 78704 tracts, using both 2000 and 2010 census figures (including the 2000 citywide averages). Between 2000 and 2010, the concentration of children declined, relative to the city average, in every single census tract.

Children were more underrepresented in 78704 in 2000 than 2010, both in absolute terms and relative to their citywide share.

Note that in 2000, 78704 had only one census tract (13.07 – Galindo) with a share of children above the city average. By 2010, though, Galindo’s share had plummeted to 80% of the city average.

Don’t make the mistake of thinking that 78704’s low share of children is due to an overabundance of VMU-style apartments, or to an overabundance of rental housing in general. Owner-occupied housing in 78704 is simply less likely to be used to raise children than owner-occupied housing in the city as a whole.

Citywide, 33% of owner-occupied homes were occupied by a household containing one or more related children under 18 in 2010. The percentages were far below that for every single ’04 census tract. The closest was Barton Hills (19.01), where approximately 25% of the owner-occupied homes contained a related child. Only approximately 18% of the owner-occupied housing in tract 13.03 (Zilker) contained a related child in 2010. Across the entire zip code, only 20.5% of owner-occupied homes contained a related child. (Comparable data is not available for 2000, unfortunately.)

I haven’t seen any persuasive evidence that the population of children in ’04 is increasing. On the contrary, we've recently heard a lot of complaints that short-term rentals are further “hollowing out” '04, making it less desirable for families with children. (I’d have more sympathy for this position if these neighborhood associations hadn’t worked so hard to make them inhospitable to larger households.)

The article cites school enrollments, but using raw school enrollment figures to track changes in population is tricky because of transfers. For example, of the approximately 380 students enrolled at Barton Hills Elementary, approximately 180 are transfers. Of course, some of these transfers are from neighboring schools. Calculating the population of school-age children requires accounting for both the source school and destination school for all these transfers, as well as homeschooled and private-schooled children. And it requires doing this for multiple years, because we're not concerned with what might be a random fluctuation from one year to the next, but an apparently long-term, secular trend. I haven't seen anyone do this analysis.

I'm also skeptical of ad hoc recounts performed by local residents. To be clear, I'm not questioning the integrity of their counts, but merely their relevance to comparisons of 2010 census counts and 2000 census counts. It's virtually certain that the census canvassers missed people in 2010 in the Zilker neighborhood, for example, but it's virtually certain that they missed people in every neighborhood in 2010, and in every neighborhood in 2000. If you want an ad hoc survey to count as compelling evidence against the decline thesis, you need a good explanation why the census takers would be more likely to miss children in 2010 than 2000.  Again, I haven't see one.

Census density data back online

I noted the other day that the Census spreadsheet with density data for all U.S. metro areas had some errors and had been taken down. A corrected version has now been re-posted.

Again, do check out the nifty graphing feature that allows comparisons between cities. Here, for example, is a graph comparing the weighted densities of  Portland and Austin at various distances from their repective city halls:

As you can see, Portland is much denser at the very center, Austin is much denser in the 1-2 mile band, and then Portland is generally much denser between the 2-mile and 13 mile marks. (The cities are pretty close between 5-7 miles).

Portland's MSA population-weighted density is roughly a third denser than Austin's. The chart above gives part of the reason -- Portland is denser across most distances. But this chart in conjunction with the last provides the full explanation:

Portland has a huge bulge in population between the 4-mile and 12-mile marks, where it is consistently more dense than Austin. So it's not just that Portland has a large swath that is denser than Austin -- that swath also happens to be where the bulk of the people live.

Why pay for it when we'll keep getting it for free?

Another data point illustrating that Austin's historic landmarking process is deeply flawed.

Last week, the Historic Landmark Commission unanimously voted to grant historic landmark zoning to Westgate Tower, the 1966-vintage condo tower between Lavaca and Colorado at 11th Street. Planning Commission and Council will vote next.

The Staff memo cites several reason for granting the designation:

• it was designed by prominent architect Edward Durell Stone;
• it is an excellent example of the New Formalism approach to modern architecture;
• it was one of the first mixed-use high-rise buildings in Austin;
• it was an early innovator in the now-standard practice of perching a condo tower on a pedestal of parking;   
• its height and proximity to the Capitol made it terribly controversial, and sparked the creation of the Capital View Corridors;
• it has been inhabited over the years by prominent state government leaders; and
• it was at one time the home of the Headliners Club.

Staff could have added that it is an excellent illustration of mid-century architectural flourishes such as the anti-pedestrian faux arcade. Here's the Lavaca streetscape:

 The Colorado arcade is just a few notches removed from a blank street wall:

Westgate Tower is thus a nice counter-example to the principle that street-fronting, ground-floor uses make for pedestrian-friendly buildings.

This is gratuitous snarkiness because I don't really quibble with the Commission's finding that Westgate Tower meets the criteria for landmark designation. It is, in fact, listed in the National Register of Historic Places. And given the very low barthe city has set for historic designation in recent years, Westgate Tower is quite significant indeed.

The fundamental problem here is not the designation itself but the consequence of the designation. The designation comes with an automatic tax break of up to $2,500 in City taxes and up to $3,500 in AISD taxes.  The staff report doesn't calculate the total loss to the city and schools from the designation -- which, frankly, is a glaring omission -- but we're talking serious money:  if the 105 condo owners receive just an average of $4,000 each, that's $400,000 in lost tax revenue per year.  

What, exactly, would we get for all this money?

The building is in no jeopardy of being demolished. Thanks largely to Westgate Tower itself, the northwestern and southeastern portions of the property are in a Capitol View Corridor and all of the property is in the height-capping Capitol Dominance Zone. It's a safe bet that no one will ever be able to build anything bigger there, and I seriously doubt whether it would be possible to squeeze in as much square footage as exists today.

I haven't tried to calculate the market value of the building. Assuming just an average of $400,000 per condo and ignoring common space and commercial space yields a total value of $41 million. In order to be redeveloped, someone would have to assume that the relatively small tract would be worth $41 million (plus cost of demolition) more with another building there. Land just isn't worth that much in Austin.

Even if someone did float a redevelopment proposal, it would have to get the assent of the condo owners. I don't know whether the condo declarations require a unanimous vote or merely a supermajority vote,  but there's no way a rational offer would ever buy near-unanimous agreement among the condo owners to sell out.

And what if someone did make a crazy offer that the condo owners accepted? Because the building is now listed on the National Register, any building or demolition permit application would automatically go to Steve Sadowski, the City's historic preservation officer, who would put a hold on it for consideration by the Historic Landmark Commission.

There is simply no credible threat that the building will be demolished. The city is proposing to give away hundreds of thousands of dollars per year to condo owners for doing nothing other than continuing to own their condos. 

The condo owners association tried to make a case that the building is under threat from rogue condo owners. From Infact Daily:

Ann Dolce, a director of the Westgate Condominium Association, said that throughout her 11-year board tenure she had seen many threats to the exterior of the building. She said the landmark designation would be a major tool to retain the design and integrity of the building.

Dolce cited as threats property owners’ requests to tint windows, install satellite dishes, enclose terraces and remove brick screening. She singled out the board’s greatest concern-- attempts by owners to purchase numerous units to obtain control and make decisions about the building.

If what we're buying is protection from minor alterations such as window tinting, then that's a pretty bad deal. Preserving the original window tinting on Westgate Tower or keeping it satellite-dish free isn't worth hundreds  of thousands of dollars per year in tax breaks. Plus, chances are any alteration that would bug me very much would bug the other condo owners a lot more.

The root of the problem is that the City (and AISD) tax breaks are not tied to the cost to the owners of preserving the property. Tax breaks grossly undercompensate the owner of a run-down building on an underdeveloped piece of property. They grossly overcompensate the owner of a property that is already being put to its approximate best and highest use. The City’s one-size-fits all compensation policy gives neither the city nor the property owners the incentive to make the right decisions.

A better system would tie the City award to the owner’s actual cost. As part of its investigation into the landmark designation, staff should estimate the cost to the owner of any extra maintenance burden and lost development rights, using clear and well-articulated criteria. The City should then award a percentage of those costs when it landmarks the property, whether in a lump-sum grant or in the form of taxes rebated over a fixed period. The County and AISD could follow suit if they want.

The size of the award, naturally, would vary with the stringency of the restrictions. We might be willing to pay someone $10,000 to preserve the building in perpetuity but only be willing to pay $10 to keep satellite dishes off the roof. A flexible system would allow us to pick and choose how much preservation to pay for.

If that were the system in place today, then landmarking Westgate Tower would not be a controversial matter. The Westgate Tower condo owners would receive only nominal compensation for agreeing not to do what they won't be doing anyway. Under the current system, they stand to make a windfall for doing nothing other than buying into a politically savvy condo owners’ association.

Austin's weighted density, 2000-2010

One of the counter-intuitive things about weighted density is, well, that it's weighted. To calculate the weighted density of, say, a metropolitan statistical area, you first calculate the density of each census tract and then assign it a weight equal to its share of the total MSA population. A census tract that has 1% of the total population is assigned a "weight" of 0.01, a census tract that has 2% of the total population is assigned a "weight" of 0.02, and so forth. The idea is that a tract with twice the population should have twice as much impact on the final average, because a person chosen at random is twice as likely to live there. (Weighted density is precisely the expected density of the census tract in which a random residents lives.)

This can produce seemingly weird results. One that surprises people is that a city can add people everywhere (and grow denser everywhere) and yet still experience a decline in weighted density.

Austin provides a nice example. The Austin MSA experienced rapid growth during the aughts, growing by 37.3 percent. But its weighted density (as calculated by the Census Bureau) dropped by 3.9%, from 3,259 ppsm to 3,132 ppsm.  

Here is a graph of the change in weighted density by distance from City Hall in downtown Austin. (I made the chart using data taken directly from the Census Bureau's Excel spreadsheet.)

Austin experienced a sharp increase in density in the center of town (0-1 miles), a steady increase in density between the 7-mile and 23-mile points, and an outright (noticeable) decline in density in only three tracts. But even these declines were relatively small.

You might be tempted to infer from this chart that Austin's weighted density rose, but you do not, in fact, have enough information to make that inference. You need to know where the growth took place. So consider this chart, which shows the population within the concentric bands at one-mile intervals from City Hall:

This chart shows that while the part of town nearest City Hall experienced healthy growth, almost all of the growth in the MSA population occurred between the 7-mile and 23-mile marks. Now, if we go back to the weighted-density graph, and draw in a line (brown) to mark the 2000 MSA weighted density, it's easy to see what happened:

Almost all of the MSA population growth occurred in the area between the black lines. But this entire area, in 2000, had below-average density, because it lies below the brown line denoting the 2000 MSA weighted density. And although the healthy population growth during the aughts pushed up its density some, it generally did not push it up to the 2000 average. Because this area now comprised a greater percentage of the total population, it received a larger weight and pulled down the average. This merely reflects the fact that a 2010 resident was more likely to live in the low-density 7-23 mile band than a 2000 resident. The MSA's weighted density accordingly declined even though the MSA added population or retained population almost everywhere.

The density profiles of Austin and Houston

The Census report I linked in the last post has just partial tables and graphs. The Bureau has a backup spreadsheet online that contains data on each metro area. It includes a nifty feature that allows you to compare the population-weighted density profiles of two cities, or even the 2000 and 2010 profiles of the same city.

For example, here is a comparison of the density profiles of the Austin and Houston metropolitan areas, based on 2010 data. Basically, the Bureau calculated the weighted density of all census tracts within 0 miles of the city halls, the weighted density of all census tracts within 1 mile of the city halls, etc., and then plotted the points.

Basically, Houston is denser in the center, Austin is denser at the 1-mile mark (because of UT and West Campus, I'm sure), Houston is slightly denser at the 2-mile and 3-mile marks, and Houston is mostly much denser between  the 4-mile and 27-mile marks.

Update: The Census Bureau has removed the Excel spreadsheet from the link. I can only speculate that it has something to do with the fact that the distance data looked wrong for some cities -- e.g., it showed weighted densities under 1,000 ppsm for Portland, OR between 4 and 14 miles from city hall, which is highly unlikely given the Portland's MSA weighted density of over 4,000 ppsm. Hopefully, they're cleaning up that data.

Austin's weighted density decreased between 2000 and 2010

The Census Bureau finally released the urban/rural components of the 2010 Census data this morning. As I suspected, the weighted density of Austin's urbanized area decreased between 2000 and 2010, from 3,904 ppsm to 3,568 ppsm. The urbanized area added a bunch of people between 2000 and 2010 but proportionately few of them settled in the denser tracts in central Austin.

I'll update the calculations for the other urbanized areas when I get the time.

The diversity of West Campus

Last week, the Daily Texan ran an interesting article entitled "A Tale of Two Neighborhoods":

The growing diversity of the UT student body has not spurred racial integration in student neighborhoods, census, city and UT records show.

The majority of Asian and white undergraduates living off campus reside in West Campus, while most Hispanic and black undergraduates live in East Riverside.

This trend has intensified in the past 10 years because of a convergence of socioeconomic inequality, disparate living costs in the two areas and alleged discrimination — and some fear it may not change.

The article marshals lots of demographic statistics to support its point that West Campus now, more than ever, draws white and Asian undergraduates while East Riverside draws blacks and Hispanics.

There's no question that West Campus is significantly less diverse than the university's undergraduate student population; blacks and Hispanics, in particularly, are badly underrepresented in West Campus, relative either to Austin's demographic profile or to the University's.

But the article spends a lot of ink on the University Neighborhood Overlay, asserting that this trend toward segregation has "intensified" despite -- or perhaps even because of -- the thousands of new beds that have been added to West Campus since the UNO was adopted in 2004.

Some perspective is in order here.

One point that ought to be made, but was somehow omitted from the article, is that West Campus is significantly more diverse today than in the pre-UNO days.

West Campus is comprised of Census tracts 6.03 and 6.04. Between the 2000 and 2010 Census counts, both tracts added minorities (including non-asian minorities) at a faster rate than nonhispanic whites.

The population count of Census Tract 6.03 rose from 5,273 to 7,793 between 2000 and 2010.

• Nonhispanic whites declined from 75.4% of the population to 65.7%
• Hispanics¹ increased from 9.3% to 12.5%
• Blacks² increased from 1.6% to 2.4%
• Asians³ incrased from 13% to 19.3%

The population count of Census Tract 6.04 rose from 5,199 to 6,496 between 2000 and 2010.

• Nonhispanic whites declined from 70.3% of the population to 59.1%
• Hispanics¹ increased from 9.4% to 13.1%
• Blacks² increased from 2.0% to 2.6%
• Asians³ incrased from 17.3% to 25%

These totals include the population in owner-occupied housing, but since owner-occupied housing contained just 5.0% and 3.2%, respectively, of the population in these two tracts in 2010 (and was not exclusively white), omitting this population would have little affect on the percentages.

Again, it is obvious that blacks and Hispanics are underrepresented in West Campus. But it should be equally obvious that the surge in population permitted by the UNO is reducing the imbalance in diversity, rather than intensifying it. Indeed, focusing on gross population changes, we see that the two census tracts added a total 3,817 residents between 2000 and 2010, only 1,188 of whom were nonhispanic whites. The two tracts added more asians than nonhispanic whites, and almost as many nonasian minorities (1,083) as nonhispanic whites (1,1888). The net result was a much greater percentage gain in the population of blacks and Hispanics (90% and 85.74%, respectively) than in the population of nonhispanic whites (17.47%). The racial balance is not ideal, but it is headed in the right direction, and that's thanks to the new housing supply allowed by the UNO. 

The Daily Texan article was less interested in the demographics of West Campus per se than in the demographics of UT undergraduates. Here's its key conclusion about the demographic trend in West Campus:

According to The Daily Texan’s analysis of demographic data sets, more than 40 percent of all white undergraduates lived in West Campus in 2010, as well as 38 percent of Asian undergraduates. Twenty-two percent of Hispanic undergraduates and 15 percent of black undergraduates also lived in West Campus then.

These numbers are significantly higher for whites and Asians than in 2000, when only 27 percent of white undergraduates and 21 percent of Asian undergraduates lived in West Campus. Fifteen percent of Hispanic undergraduates and no black undergraduates lived in West Campus in 2000.

If these statistics are reliable, then the Daily Texan has identified a real phenomenon. White students who live off-campus are roughly twice as likely to live in West Campus as Hispanics who live off campus and more than twice as likely to live in West Campus as blacks who live off campus. Again, though, its not clear that this is "worse" than in 2000 -- after all, according to the DT's "demographic data sets," no black undergraduates lived in West Campus. A rise from 0% to 15% somehow seems like an improvement. 

The Daily Texans' numbers seem plausible, but I wish the article had been more specific about the "demographics data sets" it was reviewing. For instance, it cites the 2010 American Community Survey at one point, but the one-year ACS surveys don't have census-tract level data. For census-tract level data, you must use the 2006-2010 ACS survey, which is a rolling sample conducted over a 5-year period. For tracts experiencing rapid change, it is a terribly unreliable source of data on the current state of things. For example, the 2006-2010 ACS estimate of 6.03's total population is 6,173. The 2010 census count for 6.03 was 7,793. Likewise, the 2010 census documented a decline in nonhispanic whites from 70.3% to 59.1% of the population. But the 2006-2010 ACS had the nonhispanic white share at 70.1% (+/- 6.1%).

Why the discrepancies? Because 6.03 added about 2,500 residents in the second half of the decade, and the rolling survey relied on samples taken in 2006, automatically resulting in a drastic undercount, both of new residents in general and the influx of minorities. The 2006-2010 ACS provides a statistical snapshot of West Campus that excludes much of the change wrought by the UNO.

And, of course, because the ACS is a survey, its estimates are just estimates; the margins of error are almost as important as the point estimates. 

But I can't tell whether the Daily Texan is relying on the ACS for the West Campus statistics quoted above. It might instead be using the 2000 and 2010 census counts, which tally the number of residents of each age, and making assumptions that residents of a given age group are UT undergraduates. Or perhaps the Daily Texan had access to UT student address records, which would allow for quite precise counts. I don't know. I should know, though, because the article should have disclosed its methodology and data sources more carefully.

¹Hispanic or Latino of any race.

²Black or African American, either alone or in combination with another race.

³Asian, either alone or in combination with another race.

Standard population density is a useless statistic for metropolitan areas

Standard population density -- total population divided by total land area -- is a useless statistic when applied to metropolitan statistical areas (MSAs).

For starters, it does not tell you anything you really want to know. The population density of a metropolitan area is typical of no particular place within the metropolitan area. Most of any MSA is vacant land because MSAs are made up of counties, not cities; they often include not just rural areas, but entire rural counties. Most of the population is concentrated in a relatively small portion of the land at a relatively high density. But all of that vacant land is added to the denominator, which causes the average density to be much lower than the density of the built-up urban areas -- the density at which most people live -- and much higher than the density of most of the land, which is sparsely settled.

That makes it an uninteresting statistic. It's like averaging the temperature outside on a sweltering summer day with the temperature inside a nicely air-conditioned house. You get a number, but it's not a number that tells you much about either the outdoor or indoor temperature.  

Likewise, we might be interested in the density of the built-up, settled area within a metropolitan area, and we might be interested in the percentage of the metropolitan area that has been developed, but combining the two statistics -- which is what standard population density essentially does -- erases the useful information.

A second problem with the statistic is that it does not permit reliable comparisons between cities. Standard population density is too sensitive to how boundaries are drawn. Consider San Antonio and Austin. The San Antonio MSA had a population in 2010 of 2,142,508 spread over a land area of 7,313 square miles for a standard density of 293 ppsm. The Austin MSA, by contrast, had a 2010 population of 1,716,289 spread over 4,220 square miles for a standard density of 406 ppsm.

So the Austin MSA appears to be much denser than San Antonio. But in what sense is that true? If we look merely at the urbanized areas (the contiguous, built-up urban core -- what you would circle as the "city" in a nighttime satellite photo), San Antonio's urbanized area is a bit denser than Austin's, using either weighted or standard density.  San Antonio's urbanized area contains a larger share of the metropolitan population (82%) than Austin's (79%), so the San Antonio MSA is also more centralized than the Austin MSA.

I submit that there's no meaningful sense in which the Austin metropolitan area is denser than the San Antonio metropolitan area. It's just that the San Antonio MSA was assigned eight counties while the Austin MSA was assigned five, as a result of which San Antonio has more rural counties.  The San Antonio MSA includes sparsely-populated Bandera County (standard density: 26 ppsm), which contains less than 1% of the MSA population. If Bandera County were excluded from San Antonio's MSA, its standard density would jump by more than 10%, from 293 ppsm to 325 ppsm. If rural Atascosa and Medina Counties were also excluded, then the San Antonio MSA's standard density would jump to 511 ppsm, much higher than Austin's.

Atascosa, Bandera and Medina Counties together account for only 5% of the San Antonio MSA population. But they determine whether the San Antonio MSA is 28% less dense than the Austin MSA or 26% more dense. Any statistic that fluctuates so wildly depending on whether such a small and insignificant share of the population is included is not a reliable measure of anything.

Finally, standard population density is practically useless for measuring change within a MSA over time. The reason, again, is that the boundaries are based on county (i.e., political) boundaries, which are static over time. If a metropolitan area is not assigned new counties between one census and the next, then the percentage change in standard density is exactly equal to the percentage change in population (because the denominator -- land area -- does not change). On the other hand, if it is assigned a new county, the MSA inevitably sees a dramatic increase in land area and a plunge in density . . . even if every single county in the MSA adds population (and thus density).

I see even serious urban economists like Ed Glaeser using metropolitan area densities from time to time in regressions. I wish they'd stop. Better to use weighted density or stick to urbanized areas.

 

Weighted densities of the big four Texas MSAs

Standard population density is a useless statistic for metropolitan statistical areas* (MSAs) because MSAs are defined by political boundaries (county lines) and consist mostly of vacant land. But weighted density is still meaningful when applied to MSAs. Weighted density tells you something about the density at which the typical resident lives. More precisely, weighted density is the average density of the census tracts within the the metropolitan area, weighted by population -- e.g., a census tract with 10,000 residents counts twice as much as a census tract with 5,000 residents. Alternatively, an MSA's weighted density is the expected density of the census tract inhabited by a randomly-chosen resident.

As I've explained before, weighted density does a better job than standard density (gross population divided by gross land area) of capturing our intuitive sense of density. It is counter-intuitive to say that the Los Angeles urbanized area is more dense than New York City's urbanized  area since the defining feature of the NYC urbanized area is the extreme urban density at its core. And, if you take the point of view of a person chosen at random from each of those urbanized areas, it's untrue: a person selected at random from the NYC urbanized area is likely to live in a much denser census tract than a person selected at random from the LA urbanized area.

We can calculate weighted densities for metropolitan areas as well as urbanized areas. Weighted densities are inevitably lower for metropolitan areas because they contain not only one or more urbanized areas but also a bunch of rural, low-density census tracts. The weighted average has to account for the chance that a person chosen at random lives in one of these rural tracts. But because most people in a metropolitan area live in the urbanized areas at the core, metropolitan weighted density is largely driven by the density of the urbanized area at the core, as this chart illustrates.

In 2000, roughly 80% of the Dallas, Houston and San Antonio MSA population lived within the urbanized area in the core of the MSA. In 2000, 0nly 72% of Austin's MSA population lived within the Austin urbanized area. Consequently, a random resident in the Austin MSA was more likely to live in a rural/small town census tract, which partly accounts for the lower weighted density  of the Austin MSA. (Austin's urbanized area held almost 80% of the MSA population in 2010.)

All four of the big Texas MSAs experienced rapid growth between 2000 and 2010. Note that the Austin MSA 2010 is slightly bigger than the San Antonio MSA in 2000.

Because none of the four MSA boundaries changed between 2000 and 2010, the standard population densities of the four MSA increased by the same percentages, which is one reason standard population density is such a worthless stat for MSAs.

The Dallas, Houston and San Antonio MSAs all experienced similar growth rates between 2000 and 2010. (The Austin MSA grew a bit faster.) And I assumed, before calculating their weighted densities, that they all experienced the same pattern of growth. But, after calculating their weighted densities, I don't think that's true. The Houston MSA experienced a sharp decline (-9.4%) in weighted density between 2000 and 2010. Dallas experienced a small decline (-3.77%) while Austin was basically unchanged and San Antonio saw a small increase.

The change in weighted density does not tell you anything directly about where growth is occurring or its form. But it does give you this information indirectly. We know that the central-city density tracts are the densest. A sharp decline in weighted density like we see for Houston tells us that, proportionally, a larger percentage of the population in the Houston MSA is now living in lower-density census tracts. While Houston experienced infill development in the aughts, a much larger share of the development necessarily occurred on the suburban and exurban fringes. San Antonio, which saw a slight increase in weighted density, either had proportionately more infill development, or its suburban/exurban development occurred at higher densities. Either way, it's hard to argue that San Antonio and Houston experienced the same pattern of development when their densities moved in opposite directions.

This surprised me. I expected Houston's weighted density to at least hold steady given all the infill development. But this is why we rely on numbers rather than our visceral impressions. The Census Bureau is scheduled to release the urban/rural data for census tracts this month, which will allow me to calculate weighted densities for urbanized areas. It will be interesting to see whether the changes in urbanized area densities mirror the changes in MSA densities.

 *A MSA consists of a core urban area plus any adjacent counties that have a high degree of social and economic integration with the urban core, as defined by commuting patterns.