Revised Development Projections

I've been working on a revised version of the development projection images that I did a while back.  I wrote a long post about it on Stat Chat that has the full images and some commentary on them.  Here I wanted to explain a little more of the technical background on how I made them.



How Is This Constructed?

The model starts with a random value in a Poisson distribution that simulates the likelihood of development.  This distribution captures the fact that some parcels will develop seemingly at random.  As different circumstances change, more and more areas will develop until finally the vast majority of land in an urban area will develop.  After that, some undeveloped plots will remain for a while and a few will simply never develop.

The values in this raster are then raised by adding a score based on the driving time to major employment centers.  This is because most development is and has been automobile-driven.  The shape of an urban area is highly predictable based on the driving time to an employment center.  Lastly, I reduced the likelihood of development based on the slope of the terrain and subtracted all national and state parks, wetlands, military bases, conservation easements, and local parks that were in some way preserved.  I then split this model up into planning district commissions because they roughly encompass metro areas that expand outward from a core.

The density that I used was the same density of development in the district that I was adjusting.  So if the developed areas of a planning district had a density of 1000 persons per acre, that's the density I used for the predicted new residents also.  These densities are likely to be off because of several factors.  They could be too high because, while areas have been gaining population over the last 50 years, the existing population has also been decentralizing and new residents are likely to buy the lowest density homes on the periphery.  On the other hand, they could be too low because, as areas grow in size, they become denser and each new person's marginal amount of developed area is a little smaller.  Additionally, the trend in recent years has swung the other way, as I pointed out earlier in the post.  For lack of a better model, I considered it a wash and stuck with the existing density.

Cities and driving distances:

Slope:

Conserved land:

Growth likelihood raster and planning district boundaries.  Some counties are shared by planning districts - I had to assign these to one district and deduct their population numbers from the other.

I'd be very interested to hear of ways you think this could be improved or additional factors that could be added in.  One I thought of was buffering around the Chesapeake Bay and other bodies of water to account for the attraction of living by the water.  Another is doing a more comprehensive service area just around the roads to get more of the development aligned with roads rather than "speckled" about.  The problem with that is that new developments come with new roads and you don't know where they're going to be.

MSA's and Commuting

New post on Statchat looking at the dependence of rural counties on nearby urban areas.

Percent of workers commuting to the Washington, DC area:

Wahoowa!

In Which I Acquire a New Toy

Namely - Tom Gross's cartogram script for ArcGIS. 

Virginia counties distorted to make area correspond to population:

Where you from?

Why do Hampton Roads and Northern VA seem so different from the rest of Virginia?  At the macro level, it's pretty obvious - the influence of the Federal government in DC and the military in Hampton Roads.  But it's even more obvious on this map, which shows the percentage of the population born in Virginia.  Blue means born here, red means born elsewhere:

Percentages are high in Hampton Roads - especially around military bases.  But almost the entire northern Virginia metro area is in the red.  Fewer than 30% of NoVA residents in most areas were born in Virginia.

Here's another map showing the percentage of the population born outside the U.S.  See the Weldon Cooper Center's post on immigration for more on this subject.

A few quick regressions on excel shows a pretty strong link between places that have more bachelor's degrees, more people born outside VA, and a higher income.  It's not a particularly new revelation - the more education and earning power a person acquires, the more geographically mobile they become.

Tract Facts

Nothing too special here in the way of analysis - was just curious about a few subjects so I thought I'd throw them onto a census tract map.  The roads are interstates to help you get your bearings.

Percent of population 25 years and older who have a Bachelor's degree or higher:

 Adults that are currently married:

 Percent of population who moved in the last year:

Sprawl: A Compact History

I am currently reading Robert Bruegmann's well-researched screed against the planning establishment's complaints about sprawl.  It's an excellent read and a tremendous hairshirt for all students steeped in planning school dogma.  In the end, though, his arguments succumb to many of the same historical reductions and internal contradictions that he is decrying in others.  Just a few great quotes that stuck out to me:

"It is possible that even when a small, remote star explodes, this event can reorder the entire gravitational system of a galaxy. A slight wobble in the axis of a planet can mean drastic warming in one area and cooling in another. So it is with urban systems, the main difference being that the most basic element in the urban system is the individual human being who can think and make decisions. Any change made by any member of any neighborhood affects, to some degree, everyone else in the metropolitan area."

p. 94

"The term 'sprawl' has never had a coherent or precise definition.  This has been one of the reasons it has been such a powerful polemical tool.  Thinking of it as a blank screen on which a great many people project their own feelings of discontent with contemporary urban conditions is a good way to approach the history of the anti-sprawl movement.  Because of the lack of a precise agreement about what sprawl is, individuals have been free to rally around certain broad but quite abstract concepts as a way to explain what is wrong with developments they see around them without necessarily agreeing on any specific diagnosis of the problems or any concrete set of prescriptions.  It has allowed people with radically different assumptions to find common cause."

p. 115

"The same homebuyers who might try to maximize their personal advantage in buying a suburban house are the voters who elect government officials and who push for land-use regulations that will benefit them, often at the price of other parts of the population.  Is it logical to think that landowners would suddenly act in a completely different fashion when they engage in political rather than economic transactions?  Nor is the kind of behavior that puts personal interest above community welfare peculiar to low-density settlements.  The resident of a central city who tries to block the badly needed expansion of a hospital next door to his apartment building because it would block his view is acting in a similar fashion."

p. 99

"Affluent residents of Youngstown who move to the exurban fringe are merely exploiting one of the most important assets available in the metropolitan area - a large supply of attractive land at low prices.  Although at first glance it appears that the dispersal to the edges does little other than eviscerate the central cities and displace agriculture, in many cases, the possibility of building a house on a large tract of inexpensive land in the exurban fringe is the one thing that continues to attract middle-class residents who might otherwise flee to more dynamic regions.  If, as is quite likely, Youngstown's downtown and central residential districts revive, it will not be despite sprawl but because sprawl has made it possible for the metropolitan area to retain residents during extremely difficult years."

p. 89

"In the early years of the 21st century, it appears that the forces of renewal and gentrification are becoming dominant in an increasing number of central cities.  The old 'crisis of the central city,' in which jobs were departing and property values plunging, could well turn out to have been a short-lived phenomenon...

Many smart growth activists believe that as people return to the city in greater numbers, this movement of people will create population gains and an increased density that will reduce the pressure for outward expansion.  Increasingly,  however, as affluent citizens have moved to the center, they are doing just what their counterparts have long done in the suburbs.  They have found that they can use zoning ordinances, historic preservation measures, environmental regulations, and other means to resist continued change, to control the appearance and character of their neighborhoods, and to stop densities from rising.  In city after city, the old zoning codes have been downzoned time and again to reduce the ultimate possible population and prevent existing densities from rising."

p.57-58

"What few people seemed to notice was the way the rising fortunes of the center, like their earlier decline, were directly connected to developments at the edge.  As more and more businesses and people, including even some of the least affluent members of the urban community, arrived at the urban periphery, it lost much of its exclusivity and social cachet.  The number of individuals at the very top of the social ladder who wished to buy large houses in the farthest subdivision declined dramatically in the last decades of the twentieth century.  As this happened, the central city and older established suburbs began to regain some of the luster they had lost in the postwar decades.

One of the ironies of this revival is that while central cities have traded on their 'traditional' character, much of what is most attractive about them is the fact that so many of the things that once defined them have disappeared.  The decanting outwards of all kinds of manufacturing and warehousing functions led to dramatic reduction in street congestion, truck traffic, and pollution.  This allowed city centers to become increasingly attractive to those who have the choice to live anywhere they wish in the metropolitan area and  who in previous decades might well have chosen to live in the suburbs or exurbs."

p. 53-54

- Robert Bruegmann