Population density: drawing the lines
David Seymour, on the Herald website
Auckland is already denser than New York, and most American and Australian cities. The 1.6 million people in Manhattan may live cheek-by-jowl, but not the other 20 million inhabiting the wider urban area.
An intelligent politician wouldn’t say something as apparently bizarre as this first sentence if it wasn’t true, so of course it is. The question is going to be true in what sense?
Based on the population figure, Mr Seymour is talking about the New York Metropolitan Statistical Area, aka, New York Urban Area, which has a population of 20.1 million and a population density of 724/km2[*]. The Auckland Urban Area has a population of 1.45 million and a density of 2,600/km2, and, yes, 2600 is larger than 724. However, as the scenic photos in the Wikipedia page for the New York Metropolitan Area suggest, that might not be a fair comparison.
In fact, it’s true almost by definition that the New York metropolitan area has a lower density than urban Auckland
Urban areas in the United States are defined by the U.S. Census Bureau as contiguous census block groups with a population density of at least 1,000/sq mi (390/km2) with any census block groups around this core having a density of at least 500/sq mi (190/km2). [Wikipedia, or see full legal definition]
That is, the metropolitan area is defined as the area around New York City all the way out until the local population density is below 190/km2. It’s a sensible statistical unit — the US Census Bureau wasn’t trying to make a political point about urban infill when they defined it — but it’s not the same sort of unit as Stats New Zealand’s definition of urban or metro Auckland.
So, what other comparisons could we do? We could compare the New York Metropolitan Area to the Auckland Supercity, whose population density of 320/km2 is less than half as high. That might be unfair in the other direction — the Supercity is designed with the future expansion of Auckland in mind, while the US definitions are only intended for a ten-year period between censuses.
We can’t quite do the perfect comparison of redrawing Auckland Urban Area by the US rules, because NZ Area Units are bigger than US Census Block Groups, and NZ meshblocks are smaller, but someone with more time than me could try.
We could compare the Auckland urban area to genuinely urban parts of the New York metro: Mr Seymour mentioned Manhattan (density 27,673/km2, three times that of the Auckland CBD, nine times that of the Epsom electorate) but the other four boroughs of New York City all have higher density than urban Auckland. Two of them (the Bronx, and Brooklyn) have higher density than the Auckland CBD, Queens (8237/km2) is closer in density to the Auckland CBD than to the rest of Auckland, and even Staten Island is denser than urban Auckland as a whole. In the metropolitan area but across the river from New York City proper we have Hudson County (density 5,241/km2) and Newark (density about 4500/km2). The whole of Long Island, part of the New York metropolitan area, but also known for places like Fire Island and the Hamptons, has population density 2,151/km2, not far below urban Auckland.
And finally, an alternative way to do this whole comparison, which is much less sensitive to where the lines are drawn, is to look at population-weighted densities. That is, for the average person in a city, how dense is the population near them? For the whole New York metropolitan area the population-weighted density is 12000/km2 (or 120/hectare). For Auckland it is 43/hectare. In other words, while people near the edges of the New York metro area have a lot of space, most New Yorkers don’t. The average person in the broad New York metropolitan area sees three times the local population density of the average Aucklander.
Update: * Mr Seymour tells me he was referring the the definition of metropolitan areas from Demographia, which trims some of the low-density parts of the Census Bureau definition of New York to give a population density of 1800, and agrees well with the StatsNZ definition of urban Auckland. So, while the issue about the difficult in defining things comparably is still an issue, it is less his fault than I had assumed.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Thomas,
You failed to cite the source I gave. For those interested it is here:
http://www.demographia.com/db-worldua.pdf
See Page three for a definition. They use 400 as a cut off and cite New York metro area at a density of 1800, not 724.
Of course you can play the game of comparing different standards all day but I used a standardised methodology to make the point. Wendell Cox’s methodology which applies equally across hundreds of cities worldwide is based on satelite imagery of the urban footprint. It would be incredible to think Wendell set out to give a distorted picture of Auckland when he embarked on this exercise.
I’m disappointed that you’ve put so much work into this post without acknowledging where I actually got the data, if you had you would have saved an awful lot of time. After all, you have been reading my tweets and I gave the link on twitter just this morning.
The section on definitions from Wendell’s report is pasted below for convenience.
3. URBAN AREAS: DEFINITIONAL ISSUES
An urban area (“built-up urban area,”4 urbanized area or urban
agglomeration)5 is a continuously built up land mass of urban
development that is within a labor market (metropolitan area or
metropolitan region. An urban area contains no rural land (all
land in the world is either urban or rural). In some nations, the
term “urban area” is used, but does not denote an urban area
as a built-up urban area.6
An urban area is best thought of as the “urban footprint” — the
lighted area that can be observed from an airplane (or satellite)
on a clear night. National census authorities in Australia,
Canada, Denmark, Finland, France, the Netherlands, Norway,
Sweden, the United Kingdom and the United States designate
urban areas. Except in Australia, the authorities use a minimum
urban density definition of 400 persons per square kilometer (or
the nearly identical 1,000 per square mile in the United States).
8 years ago
The prime mover behind Demographia is a sceptic about public transport options and smart (i.e. managed intense) urban growth. He is associated with the Heritage Foundation and Cato Institute. This does not necessarily make his stats wrong, but one would suspect that they are massaged to suit his ideological predelictions.
8 years ago
He does, however, have quite a reasonable definition of the New York metropolitan area, and a comparable definition for Auckland. That’s all *I’m* claiming.
Population-weighted density is a clear winner as far as I’m concerned.
8 years ago
Seymour says: ‘It would be incredible to think Wendell set out to give a distorted picture of Auckland when he embarked on this exercise.’
Well, indeed, I doubt Cox spends much time thinking about Auckland, because after all he is paid to make claims about north american cities: He is a lobbyist for the sprawl industry there. But disingenuity about density is his stock and trade. In fact his entire career is about averaging out density figures to meaninglessness.
Which of course leads to abject nonsense like the claim by Seymour that Auckland is more dense than New York.
Hilariously for Seymour Cox is usually all about trying to show that no North American metro has sufficient density to support Transit systems, hence the low number cooked up for New York. A place which would of course entirely infarct without its existing Transit Networks. So will the Transit hating Seymour later turn around to claim that Auckland has a density too low such systems, or stand by his claim for this city’s world beating high density?
Do tell David?
8 years ago
I didn’t know population-weighted density. It’s a very interesting concept.
Anyway, I wish to know something more about it. I have made some calculus realizing that it depends on the granularity of the city dissection.
So, can you tell me if there is a defined standard squared block whereby population-weighted density is computed and how large it is?
Thank you for your blogging.
8 years ago
There isn’t, but you can do it with individual households, and doing it with NZ census meshblocks isn’t going to be much worse.
8 years ago
And what about New York?
Maybe I haven’t been able to explain myself.
Supoose I have to compute the density of a very large city. It holds that:
1) density is always smaller than
2) population-weighted density using as a unit a block of 10 km2 which is always smaller than
3) population-weighted density using as a unit a block of 5 km2 which is always smaller than
4) population-weighted density using as a unit a block of 2 km2 which is always smaller than
5) population-weighted density using as a unit a block of 1 km2.
So, if I want to obtain the highest density I have to use the thinnest grid.
To compare densities for two cities a similar argument apply. Ah honest comparison needs to refer to the same grid for both the cities.
Are Auckland quarters comparable to New York quarters in terms of size (km2)?
8 years ago
You’d have to look it up. But note also that there doesn’t even have to *be* a grid. The locations and sizes of households are known, and the population-weighted density is definable without reference to a grid (eg, as the integral of the square of the density function)
A smoothing bandwidth of some sort is needed for *estimation*, but that’s a different issue.
8 years ago
Also, if there is a grid, it’s more likely to be roughly constant population rather than roughly constant area — US Census blocks or NZ meshblocks.
8 years ago
It may be a bit late to the discussion but the OECD is a good place to look for discussion on this topic. They provided a classification in the 1990’s for OECD members to use and seems to the basis of most further work. The OECD hosted a conference in 2006 to further examine this this topic, to which Statistics NZ contributed. For a recent Eurostat discussion see http://www.nidi.nl/shared/content/output/papers/nidi-wp-2014-03.pdf
The key learning is that it is never going to be a clear urban / non-urban split, but rather a continuum and where you set you cut-off is a bit of a subjective topic.
As an aside, one change I’ve noted over my 30 years as an official statistician is the acceptance that classification is rarely simple or easy to standardise. It is now even generally accepted that a male/female split is not always helpful for understanding what the data is telling you.
8 years ago