The single greatest challenge to any type of land value taxation system is accurate valuation of land on a large scale. In urban areas where nearly all real estate sales data represent transfers of land with improvements, it is difficult to divide prices between land and building components. Although many jurisdictions require a separate listing of land and building values on their tax rolls, these allocations will not affect the final tax bill if the tax rate is the same on both.

Any special tax on land value alone would increase the need to assign more accurate land values to parcels that have been improved over many years. As a result, skepticism as to the feasibility of this process has proven a major stumbling block to serious consideration of two-rate property taxes and other forms of special land taxation. Many observers have concluded that the practical problems of land assessment prevent the realization of the many theoretical benefits it offers.

New advances in computerized approaches to property assessment have important implications for this debate. While land valuation presents special problems in the analysis of sales data for improved parcels, it also can benefit from location analysis and land value mapping techniques. Buildings can and will vary unpredictably in both type or value from lot to lot, but land values for adjoining or nearby parcels should have a more constant relationship to one another. More than 20 years ago, Oliver Oldman of Harvard Law School, considered the implications of this situation for an appeals process under a land value tax, recognizing that a successful challenge to one parcel’s valuation would have implications for many other assessments as well. He wrote, “The key to developing an accurate land-value assessment roll is the process of land-value mapping.” Now the technology is available to achieve this goal.

In a recent seminar at the Lincoln Institute, representatives of the Auditor’s Office in Lucas County, Ohio, which includes the city of Toledo, joined a group of economists, appraisers, lawyers and local officials to examine current methods of land valuation. Lucas County has one of the most sophisticated appraisal systems in the country, with almost 20 years of experience in using computerized methods of spatial data analysis for property taxation. The seminar provided a valuable opportunity to discuss the county’s innovative approaches to the integration of geographic information systems and computer-assisted land valuation to estimate the effect of location on real estate market value.

Traditional Methods of Land Valuation

There are several standard methods of deriving a value for unimproved land, all extremely problematic as the basis for jurisdiction-wide assessment.

Comparable Sales: The most straightforward method is an analysis of sales of comparable unimproved land, adjusting the prices to account for any differences in size, location, and features. Similarly, the capitalization of rental income for comparable vacant land can serve as a basis for estimating its sale price. However, these methods are difficult to apply in densely populated urban areas where sales or rentals of unimproved land are rare. The pool of sales data can be expanded if sales of improved land are followed soon after by demolition of the buildings. In that case, the unimproved land value can be estimated as the purchase price minus the costs of the demolition. Although such sales provide an important check for estimated values produced by other approaches, they do not exist in sufficient numbers over a varied enough geographic range to serve as the sole basis for assessment.

Income Analysis: The land residual method begins with an estimate of the income yielded by the developed property. The building value is then calculated, and from that the income attributable to the building is derived. Capitalizing the remaining income then provides a value for the land. However, even a cursory description of this method suggests the difficulties of its application. In particular, the existence of depreciation, or any deviation from highest and best use that would distort the income available to the unimproved land, can leave the independent value of the improvements extremely uncertain.

Cost Analysis: Similar problems confront a division of value according to the depreciated reproduction cost of the improvements. This method assumes that structures can be worth no more than their cost of construction, and assigns all remaining value in the improved parcel to the land itself. Physical, economic or functional depreciation greatly complicates the attempt to calculate building value, however, so this method requires fairly new construction whose price can be confidently estimated as a measure of value. The financial effect of various forms of obsolescence can only be measured accurately through examination of sales data, which will almost never be available for the building alone.

Cost of Development: A full-scale market appraisal of potential development alternatives provides another basis for estimating the sale price of unimproved land. This is the approach taken by developers considering new uses for land, land trusts seeking to acquire and preserve undeveloped open space, and taxpayers claiming deductions for charitable contributions of development rights. However, it is most suitable for valuing undeveloped land to be used for residential subdivisions. Even in these situations, it requires extensive study of the potential market for such properties, local restrictions on development, and the physical attributes of the land that would affect its building capacity, such as soil and drainage characteristics. This type of exhaustive individual appraisal is appropriate for purchasers or developers of individual parcels, but is not feasible for annual assessments for all parcels in a taxing jurisdiction.

Other valuation methods, such as derivation of typical ratios of site value to total improved property value, are even less useful in the case of densely developed urban property, where buildings of all sizes, ages and utility may be found in close proximity on fairly similar parcels of land.

New Approaches: CAMA and GIS

The greatest change in assessment practice over the past three decades has involved the use of computers and mathematical formulas to establish a relationship between property characteristics and sale prices, thereby permitting an estimate of the market value of other properties not subject to a recent sale. This approach is known as computer-assisted mass appraisal (CAMA). Site characteristics such as size and location are important elements of these mathematical models, raising the possibility of estimating the effect of location on parcel value.

At the same time, the development of computerized geographic information systems (GIS) has permitted assessors to develop location-based property records or cadastres, and to coordinate sales data with location. More sophisticated and less expensive GIS technology now offers the potential for full integration with CAMA for spatial analysis. Initial attempts to quantify location effects faced difficulties not only in defining and maintaining “economic neighborhoods” or zones, i.e., contiguous areas of relatively homogeneous land values, but also in understanding the dynamics of the interactive, elusive locational factor. Some efforts developed different mathematical models for each geographic region or “cluster” of properties with similar characteristics. However, these approaches could not capture the many complex, interrelated and significant micro-variations within any given neighborhood, and could not reduce the determination of location value to an objective process.

Lucas County pioneered a new approach to location value-the use of GIS tools to develop a response surface that represents the effect of location on land value. The response surface is a fitted three-dimensional surface that represents a percentage adjustment to land and/or land and improvements based on a parcel’s geocoded location. Included in the analysis are geographic coordinates and distances from important features, such as other recent sales, institutions, amenities or other “value influence centers.” This analysis results in a three-dimensional representation, with the height of the surface (z) at any specific x-y coordinate indicating the approximated location value of that parcel. This variable is then evaluated with others, such as land and building size, quality, condition and depreciation, to produce a total estimated value for the parcel.

In the Lucas County example, the response surface differs from a mathematical equation in that it is developed through a spatial analysis process available in GIS to estimate the effects of location on value and refine those estimates after comparing them with sales and appraisal data. This approach still relies on an element of appraisal and economic judgment in determining neighborhood boundaries for location effects, but it can be tested and refined by observing the effect of different neighborhood “breaklines” on the resulting three-dimensional value surface.

To be used successfully in mass appraisal, these sophisticated approaches must yield results that are reasonable, understandable and available to typical taxpayers. Lucas County has pioneered this aspect of the assessment process, as well. All real estate records, values and maps are available on a CD with GIS viewing software, priced at its production cost of $10, and online free at all public libraries in the county. Taxpayers can view property records or create customized maps showing the location of multiple parcels and the relationships among their taxable values.

Future Directions

Participants in the Lincoln Institute seminar found great promise in the Lucas County approach to location value, and identified many points for further development and investigation. All agreed that recent decades have seen a literal revolution in assessment practice, with great potential for increasing the feasibility of large-scale land valuation. Among the most important theoretical questions were the “functional form” of this spatial analysis, including the type of effect on value observed with changes in location and distance variables; the identification of omitted variables (those for which data is not available or which have been overlooked in the past); and the relationship between marginal value estimates and the total parcel value needed for assessment. Similarly, the effect of substandard buildings and less than “highest and best use” on values requires further exploration.

Development of these new approaches must be matched by educational efforts to explain their operation to taxpayers, local officials, and the lawyers and judges who will consider their consistency with legal standards for assessment practice. Through its innovative efforts in both of these areas, Lucas County has made an important contribution to the theory and practice of land valuation.

Jerome C. German is the chief assessor for Lucas County, Ohio. Dennis Robinson is vice president of programs and operations at the Lincoln Institute. Joan Youngman is senior fellow and director of the Institute’s Program on Taxation of Land and Buildings.

References

International Association of Assessing Officers. Property Appraisal and Assessment Administration (1990).

Oliver Oldman and Mary Miles Teachout. “Valuation and Appeals Under a Separate Tax on Land.” 15 Assessor’s Journal 43-57 (March 1980).

Richard D. Ward, James R. Weaver, and Jerome C. German. “Improving CAMA Models Using Geographic Information Systems/Response Surface Analysis Location Factors.” 6 Assessment Journal 30-38 (January/February 1999).

Lucas County website: www.co.lucas.oh.us

It’s a Thursday afternoon in Cincinnati, and people at the downtown public library are making stuff. In the corner, a $14,410 Full Spectrum laser cutter and engraver hums away, used to create anything from artworks to humble coasters out of paper, wood, and acrylic. Over by the windows, a MakerBot replicator is buzzing; it’s one of the library’s four 3-D printers, used to fabricate a range of objects, from toys to a custom bike pedal compatible with shoes designed for a patron with a physical disability. Nearby, a young designer is producing a full-color vinyl sign with a professional-grade Roland VersaCAMM VS-300i large-format printer and cutter. “This is our workhouse,” my tour guide Ella Mulford, the library’s TechCenter/MakerSpace team leader, says of the $17,769 machine. Most of us couldn’t afford such a pricey piece of equipment, but apparently plenty of Cincinnatians can think of useful things to do with it: it runs practically nonstop during library hours, Mulford explains, and is usually booked out for two weeks in advance. 

The Public Library of Cincinnati and Hamilton County still offers plenty of books and other media for borrowing and browsing. But its roomy MakerSpace section, opened at the start of 2015 and packed with free-to-use tech tools, is an impressive example of how the library idea is adjusting to a digital era that has not always been kind to books. More to the point, it hints at an evolving role for libraries in cities large and small—contributing in new ways to the municipal fabric they have long been a part of. 

In Cincinnati, the process that led to the MakerSpace started a couple of years ago, says Kimber L. Fender, the library’s director. A smattering of libraries across the country were experimenting with technology as a new component of what they might offer the public. “And part of our strategic plan,” Fender continues, “was to introduce new technologies to our community. So we were actively exploring: What does that mean when we say that? What does it look like?” Adding a 3-D printer to the library’s existing computer center served as a low-risk experiment—and attracted the attention of every TV station in town. “There was just all this conversation,” Fender recalls. “So we thought, ‘Hm, this is getting us toward our goal.’” 

Enrique R. Silva, research fellow and senior research associate at the Lincoln Institute of Land Policy, points out that there’s no real reason to yoke the fate of the library as civic infrastructure to the fate of the physical book. “It’s a community space for learning,” he suggests. A 2015 Pew Research Center study indicates that the public agrees: While it found signs that Americans have visited libraries somewhat less frequently in recent years, it also concludes that many embrace the idea of new educational offerings in this specific context—tech included. “It’s not a difficult leap to make,” Silva says.  

Indeed, making that leap both extends and updates the role that libraries have long played in many U.S. city and town plans. One of the breakthrough developments in that history was the explosion of such institutions funded by Andrew Carnegie in the decades before and after the turn of the 20th century. Fanning out from Pennsylvania, nearly 1,700 so-called Carnegie Libraries were built in Beaux-Arts, Italian Renaissance, or other classic styles—an effort that both played into and fueled an even wider library-building movement that placed significant landmarks in municipal centers from coast to coast. While remarkable, this ubiquitous element of civic infrastructure often goes overlooked today. 

“In modern-day planning,” Silva observes, “I think libraries are largely seen as: You’re lucky if you have it as an asset, part of the bones of a city that you work around.” In the United States, at least, architecturally significant new library construction is rare (the Seattle Public Library Central Library, opened in 2004 and designed by Rem Koolhaas and Joshua Prince-Ramus, is a notable exception). So libraries tend to be planned around, as an “inherited” element of “social-civic infrastructure,” as Silva puts it. A 2013 report from the Center for an Urban Future, focused on New York City, argued that libraries have been “undervalued” in most “policy and planning discussions about the future of the city.”

But maybe this oversight implies an opportunity: These existing structures can take on fresh roles that make them newly relevant to ever-evolving municipal plans. The Cincinnati library’s rethink of what it means to be a community center of learning and information-sharing is one example. As with the Carnegie Libraries, smart use of philanthropic resources played a role: Fender says the library had a $150,000 discretionary bequest that it decided to direct to the MakerSpace. To make room, it reorganized its periodicals collection. 

The library then took an adventurous view of what kind of technologies it could offer. There’s a mini recording studio with pro-quality microphones, used by aspiring podcasters and DJs; photography and video equipment; and a popular “media conversion station” for digitizing VHS tapes and the like. There are also more analog offerings such as sewing machines and a surprisingly popular set of button-making machines. During my tour, I met a charming man named Donny—well known to the library staff—making football-themed buttons. “What’s the word, ‘entrepreneur’? That’s what they tell me I am,” he explained. 

Turns out lots of entrepreneurial types, from aspiring startup-founders to Etsy sellers, make use of the library’s offerings. There are collaborative computer workstations, connected by Wi-Fi and used by everyone from designers working with clients to students teaming up on class projects. 

And there’s a broader trend here. The Chattanooga Public Library has converted what used to be the equivalent of attic space into a maker center and public tech lab called 4th Floor, regularly hosting related public events. The Sacramento Public Library’s “Library of Things” allows people to check out GoPro cameras and tablet devices, among other tech tools. Other experiments abound from Boston to St. Louis to Washington, DC, to Chicago: according to one survey, more than 100 libraries had added some variety of makerspace as of 2014; another report said more than 250 have at least a 3-D printer available.

And the progressive thinking and creativity of libraries align with the goals of many planners: maintaining and exploiting community touch-points, often embedded deep into crucially central public spaces, and expanding the range of citizens drawn to them. Interestingly, some urban thinkers have begun to explore the potential of makerspaces arising either from the private sector or the grass roots as a component of “a new civic infrastructure.” Perhaps libraries like Cincinnati’s are already building that. 

One challenge, Fender says, is the lack of widely accepted metrics for gauging the impact on a given institution—or, by extension, its civic environment. So Cincinnati has been keeping its own numbers: in September 2015, the MakerSpace took 1,592 equipment reservations, including 92 for the MakerBot, 157 for the laser engraver, and 298 for the vinyl printer. All reflect steady or growing interest. (Thus the MakerSpace collection is growing, with the addition of an Espresso Book Machine that prints volumes on demand.) 

“The MakerSpace reminds people the library is there,” Fender says, “but it also causes them to look at it in a different way and say: ‘Oh, they’re thinking about the future, about what the community needs are, and how they can provide something more than the books on the shelf.’” 

Rob Walker (robwalker.net) is a contributor to Design Observer and The New York Times.

Photograph credit: The Public Library of Cincinnati and Hamilton County

For years, it looked like the next big thing in public transportation for the suburban city of Altamonte Springs, Florida, would be an innovative program called FlexBus. Instead of running on fixed routes, buses would respond to demand from kiosks located at specific activity centers. It was, city manager Frank Martz says, “the first demand-response transportation project ever developed in the United States.” Some even referred to it as an “Uber for transit.”

Unfortunately, it didn’t work out. The regional bus operator administering the plan lost key federal funding, and Altamonte Springs had to look for a new solution. “Rather than be mad,” Martz continues, “We decided to solve the problem. We still needed to serve our residents.” 

This time, officials went with Uber itself. This past spring, the Orlando suburb announced a straightforward partnership with the ride-sharing firm, subsidizing citizens who opted to use that service instead of their own cars—particularly for trips to regional rail stations that connect population centers around Seminole County. The pilot has proven popular enough that several municipalities in the area have already launched similar programs. 

Most of what we hear about the relationship between municipalities and ride-sharing startups involves contention. Right around the time Altamonte Springs started this pilot program, a standoff over regulatory details in Austin, Texas, led both Uber and its chief rival Lyft to stop doing business in the city. But Altamonte Springs is an example of how some cities, planners, and scholars are trying to find opportunities within the rise of ride-sharing’s prominence and popularity. MIT’s Senseable City Lab has worked with Uber; UC Berkeley’s Transportation Sustainability Research Center and others have been diving into ride-sharing data with an eye toward public-transportation impacts. And this past March, the American Public Transportation Association released a study assessing how new services can complement more familiar forms of “shared mobility,” and suggested ways that agencies can “promote useful cooperation between public and private mobility providers.” 

“What it’s going to boil down to is how this new system interacts with the existing, traditional system,” says Daniel Rodriguez, a Lincoln Institute fellow who teaches planning at University of North Carolina and has studied transportation innovation in Latin America and the United States. He expects more experiments as cities work to figure out how “to get Uber users to complement the existing infrastructure.” 

That almost exactly describes one of the prime motivations for Altamonte Springs’ Uber pilot: the service was, Martz points out, an existing option that required none of the time-and-money commitments associated with a typical transportation initiative. “The focus could not and should not be on infrastructure,” he said. “It needed to be on human behavior.” In other words, ride-sharing services already respond to demand that has been demonstrated by the market, so how could the city hitch a ride on that trend? 

The answer was to offer local users a subsidy: the city would pay 20 percent of the cost of any local ride, and 25 percent for rides to or from Sun Rail stations, the region’s commuter-rail system. Riders simply enter a code that works in concert with Uber’s “geofencing” technology to confirm location eligibility; their fee is lowered accordingly, and the city seamlessly makes up the difference. “It’s all about user convenience,” Martz says. But he’s getting at a bigger point than ease of payment. Instead of building systems that citizens respond to, maybe it’s worth trying a system that responds to where citizens actually are—and adjusts in real time as that changes. 

Whether this works out in the long run remains to be seen, but as an experiment the risks are pretty low. Martz has estimated the annual cost to the city at about $100,000—compared to $1.5 million for the earlier FlexBus plan. While the pilot is just a few months old, he says local Uber use has risen tenfold—which is why neighboring municipalities Longwood, Lake Mary, Sanford, and Maitland have all joined in or announced plans to do so. (“We’re creating a working group among our cities,” Martz adds, with a focus on managing traffic congestion and “how to connect our cities.”) 

As Rodriguez points out, the land-use implications alone, both short- and long-term, are compelling. On the day-to-day level, affordable ride-sharing as an option for, say, doctor visits or school appointments or similar errands lowers demand for parking spaces. On a higher level, it leverages options that already exist instead of devising more land-intensive projects that can take years to plan and complete.

In a sense, the experiment fits into a broader trend of seeking ad-hoc transportation innovations. Rodriguez has studied experiments from home-grown bus systems to aerial trams in Latin America that supplemented existing systems rather than building new ones. And while at first blush the concept of partnering with a ride-sharing service sounds like something that would work only in a smaller municipality that lacks a realistic mass-transit-system option, he points out that it could actually play a role in bigger cities. One example: Sao Paulo, Brazil, which offers what The Atlantic’s CityLab has called “the best plan yet for dealing with Uber”—essentially auctioning off credits, available to both existing taxi services and ride-sharing upstarts, to drive a certain number of miles in a set time period. The regulatory details (devised in part by former Lincoln fellow Ciro Biderman) aim to give the city options, while capturing and exploiting market demand rather than trying to shape it. 

That captures Martz’s broader attitude. “Why,” he asks, “should the public sector focus on infrastructure embraced by people who used it 40 years ago?” While he readily notes that this line of policy thinking is very much in step with the pro-free-enterprise attitudes in “a very Republican county,” he also insists that local political support for the plan crossed party lines. And more significantly, he stresses that this solution leaves the city much more easily positioned to adjust as technology changes. Carpooling scenarios seem like one logical possibility. And Uber and other technology companies are known to be working on driverless-car scenarios that could prove even more efficient. Martz doesn’t quite come out and say this, but if Uber gets “disrupted” by some more efficient solution, striking up a new partnership would be a lot easier than a do-over on a multiyear region-wide project. “Let market forces carry the day,” Martz says. 

Of course, as Rodriguez notes, all of this remains very experimental at this stage—and a full-on embrace of ride-sharing carries potential downsides. It obviously remains car-centric and not necessarily affordable to broad swaths of many city populations, even with the 20 percent discount. The ability to travel longer distances for lower costs has been a major factor in city sprawl. “This could be another step in that direction,” he observes. 

But the combination of uncertainty and potential is exactly why it’s worth attending to efforts that embrace ride-sharing upstarts instead of fighting them. “There’s no correct answer right now; it’s still an exploration,” Rodriguez cautions. But the likes of Uber do offer one attribute that’s hard to deny for those willing to experiment, he adds: “It’s tangible, and you know it works.” 

Rob Walker (robwalker.net) is a contributor to Design Observer and The New York Times.

In his 1937 essay “What is a City?,” Lewis Mumford described an evolutionary process through which the “badly organized mass city” would evolve into a new type of “poly-nucleated” city, “adequately spaced and bounded”: 

“Twenty such cities, in a region whose environment and whose resources were adequately planned, would have all the benefits of a metropolis that held a million people, without its ponderous disabilities: its capital frozen into unprofitable utilities, and its land values congealed at levels that stand in the way of effective adaptation to new needs.”

For Mumford, such cities, designed with strong public participation, would become the nuclei of new poly-nucleated metropolitan regions that result in:

“A more comprehensive life for the region, for this geographic area can, only now, for the first time be treated as an instantaneous whole for all the functions of social existence. Instead of trusting to the mere massing of populations to produce the necessary social concentration and social drama, we must now seek these results through deliberate local nucleation and a finer regional articulation.”

Unfortunately, since Mumford wrote these words, we have not achieved poly-nucleated cities or regions. Nor have we advanced a theory of urban evolution. Urban theorists have described cities, used basic pattern recognition to detect relationships among the potential components of urban evolution, or offered narrow prescriptions to fix one urban challenge while generating inevitable unintended consequences that pose new challenges. This is because we have never developed a real science of cities. 

For more than a century, planners, sociologists, historians, and economists have theorized about cities and their evolution by categorizing them, as noted by Laura Bliss in a well-documented 2014 CityLab article about the likelihood of an emerging evolutionary theory of cities. They generated multiple typologies of cities, from functional classifications to rudimentary taxonomies (see Harris, 1943, Functional Classification of Cities in the United StatesAtlas of Urban ExpansionAtlas of Cities). But they based these classifications on arbitrarily chosen categories and did little to inform our understanding of how cities became what they are or to presage what they might become. 

Even Jane Jacobs, in a foreword to her 1961 book, The Death and Life of Great American Cities, called for the development of an ecology of cities—a scientific exploration of the forces that shape cities—but provided only narrative accounts of what defined great cities, mostly with regard to design, as part of her ongoing assault on the orthodox planning profession. In some of her later work, Jacobs set out principles to define great cities, based mostly on form, but she never provided a framework to improve the science of urban theory.

Modern urban theory is plagued by several shortcomings. It is not analytic. It fails to provide a framework for generating hypotheses and the empirical analysis to test those theories. And the research, in general, focuses on big iconic cities, rather than a representative global selection of urban settlements that captures the differences between big and small cities, primary and secondary cities, industrial and commercial cities. Importantly, the research provides little guidance regarding how we might intervene to improve our future cities to support sustainable human habitation on the planet. 

The New Urban Agenda—to be announced in October at the third UN-Habitat conference, in Quito, Ecuador—will present consensual global objectives for sustainable urbanization. These objectives provide guidance for United Nations member states as they prepare for the gargantuan task of welcoming 2.5 billion new urbanites to the world’s cities over the next thirty years—culminating the 250-year process through which human settlement moved from almost entirely rural and agrarian to predominantly urban contexts. But before we attempt to implement the New Urban Agenda, we must confront the serious limitations in our understanding of cities and urban evolution. A new “science of cities” would buttress our efforts to get this last stage of urbanization right.

I do not intend to present a new science of cities in this message. Instead, I will suggest a way to frame one that borrows from evolutionary theory. The evolution of species is driven by four main forces, and it seems reasonable that corollary forces help to shape the evolution of cities. These forces are: natural selection, gene flow, mutation, and random drift. And they play out in predictable ways that shape cities—where city growth replaces reproductive success as an indicator of evolutionary success.

Natural selection is a process of impulse and response. It relates to how a city responds to changing external factors (impulses) that support or inhibit success. Impulses can be economic, environmental, or political, but they are, importantly, outside the control of the city. Economic restructuring, for example, might select against cities that depend on manufacturing, have inflexibly trained workforces, or extract or produce single commodities that face changes in demand in global markets. Climate change and sea-level rise will inhibit the success of coastal cities or those exposed to severe weather events. Political impulses might include regime changes, social uprisings, or war. Or they might be something as seemingly minor as a change in allocation formulae for national revenues. Every impulse will benefit some cities and harm others. A city’s ability to respond to different impulses might be a measure of its resilience, which is directly influenced by the three other evolutionary forces. 

Migration (gene flow) helps to diversify the economic, social, and age structures of cities through the exchange of people, resources, and technologies. Presumably, the in-migration of people, capital, and new technology improves a city’s ability to respond to external impulses. Out-migration, in general, would reduce this ability. 

Mutation, for cities, is an unpredictable change in technology or practice occurring within a city. It might be shorthanded as innovation or disruption. 

Random drift involves longer-term changes in cities that result from cultural or behavioral shifts. These might include decisions to maintain or preserve long-term assets, real or cultural. Drift describes the unpredictable ways that cities might change their character. 

As noted, I do not want to lay out a new theory of urban evolution here. I merely want to recommend this direction in order to invigorate our thinking around urban change more rigorously and systematically. A significant amount of work has already gone into quantifying elements of this framework. Risk theorists and insurers have quantified many of the external impulses that challenge cities. Demographers and population theorists have studied human migration, and macroeconomists have studied capital flows. A lot of attention has been paid to innovation and disruption in the last couple of decades. Random drift is a little less studied. But, as Bliss points out, big data and new technologies might help us to detect longer-terms drift. In any case, a larger framework that weaves these disparate areas of work together would advance our understanding of urban evolution. 

On a cautionary note, while an evolutionary theory of cities would be a signal advancement of urban theory, it is useful to remember that, unlike evolution, which is a mostly passive process—species enduring the external forces that act on them—cities, in theory at least, are driven by more purposive behavior: planning. But planners need better tools to drive their practices and to test their approaches. If we are to successfully implement the New Urban Agenda, a toolkit based on evolutionary science would be hugely helpful. As Mumford concluded in his 1937 essay:

“To embody these new possibilities in city life, which come to us not merely through better technical organization but through acuter sociological understanding, and to dramatize the activities themselves in appropriate individual and urban structures, forms the task of the coming generation.”

We at the Lincoln Institute of Land Policy stand ready to support coming generations in comprehensive and scientific analysis of urban evolution and the important role that effective land policies can play in driving it. Our urban future depends on it.