2 de julho de 2012

Quantitative analysis of urban form: a multidisciplinary review

Journal of Urbanism: International Research on Placemaking and Urban Sustainability
Volume 1, Issue 1, 2008

Kelly Clifton, Reid Ewing, Gerrit‐Jan Knaap & Yan Song


This paper characterizes and reviews multidisciplinary approaches to urban form. It begins by classifying quantitative approaches to analyzing urban form into five classes: landscape ecology, economic structure, surface transportation, community design, and urban design. It then reviews quantitative measures in each class. Based on the review, four conclusions are drawn. First, over the last two decades substantial progress has been made in the ability to measure and analyze spatial patterns that help characterize urban form. Second, at multiples scales and for a variety of reasons, there are advantages to development that is mixed and compact. Third, normative principles and policies for addressing urban form need to be crafted at multiple scales and carefully designed to address the disparate issues that arise at each scale. Fourth, with so many disparate measures now used to operationalize the same constructs, it would advance urban form research to have some standardization in operational definitions and measurement protocols.

• Abstract
• Introduction
• Landscape ecology
o Patch characteristics
o Landscape composition
o Configuration and diversity
o Research on urban form based on measures of landscape ecology
• Economic structure
o Metropolitan size, density, and diversity
o Metropolitan structure
o Polycentricity
o Research on form at the metropolitan scale
• Transportation planning
o Network configuration
o Density and diversity
o Accessibility
o Research on sprawl at the sub metropolitan scale
• Community design
o Composition and arrangement
o Transportation networks and accessibility
o Categorical and composite distinctions
o Research on sprawl based on community design
• Urban design
o Physical features
o Accessibility
o Perceptions
o Integrated measures of urban design and urban perceptions
o Research on sprawl at the urban design scale
• Conclusions
• Notes
• References


Although interest in urban form is not new, this review suggests that scholars have made considerable progress in developing and computing measures of urban form. These measures capture spatial arrangements at varying scales, use data from a variety of sources, and address concerns that confront multiple disciplines. Efforts to conceive and compute these measures, however, are not solely for academic interest. Quantitative analyses that use these measures have and will continue to inform public policy from the landscape to the urban design scale. But getting the policy right requires a thorough understanding of what is being measured, how that measurement affects social welfare, how what kind of policy response is required.

Interest in urban form – or urban sprawl – is strong among scholars trained in multiple disciplines. Further, the issues of concern to the various disciplines often dictate the scale of analysis, the specific phenomena of interest, and often the source of data. These systematic differences between disciplines, it is argued, define distinct perspectives on urban form and approaches to measurement and quantitative analysis. Too often, it is believed, principles of urban form are proposed without due consideration of multidisciplinary perspectives and the scales at which such perspective might be most pertinent.

Research on urban form at the regional scale, often conducted by landscape ecologists and other natural scientists, is generally concerned with species habitat and ecological processes. The evidence suggests that urban sprawl indeed disrupts habitat and, due to the expansion of impervious surfaces, degrades water quality in streams, lakes, and rivers. To minimize these effects, it is clearly desirable for the urban footprint to remain as small as possible. Thus, from a landscape perspective, and holding other things constant, preferable urban forms are compact, contiguous, and generally circular. Such development patterns minimize not only imperviousness and habitat conversion, but also habitat and watershed fragmentation. Appropriate public policies from this perspective include urban containment instruments – such as urban growth boundaries – and surrounded by green spaces, critical habitats, and ecologically sensitive land with special protections.

Research at the metropolitan scale, largely by economists, focuses on city size and structure. The evidence suggests that economic benefits accrue to urban size and diversity. Even after adjusting for differences in the cost of living, incomes tend to be higher in cities that are large and diverse. These findings support economic development strategies that favor attracting a diverse set of industries to existing cities. The evidence also strongly suggests that land uses and development intensities vary systematically with land prices. In a monocentric model this implies downward sloping density and intensity gradients from a single, central node; in a polycentric model, this implies the same for multiple nodes. Economists define good urban form as that which maximizes social welfare. Economists, therefore, tend to favor policies that change relative prices and incentives to internalize externalities yet allow the market to work without regulatory distortion – like priority funding areas, impact fees, and taxation.

Research on urban sprawl at the submetropolitan level, generally conducted by transportation planners, focuses on accessibility. Urban sprawl from this perspective increases the distance between origins and destinations. To maximize access, it is clearly preferable for urban growth to be compact and contiguous. Further, within urban areas, transportation planners prefer that subregions are well connected and contain mixed uses both to minimize the impedance between submetropolitan zones and to promote travel within such zones. Policies favored by transportation planners thus include those that increase the connectivity of the network, channel growth in highway and transit corridors, and concentrate mixed‐use developments within those corridors.

Research on sprawl at the community level, generally by urban planners, addresses a variety of concerns. Like landscape ecologists and transportation planners, urban planners care about environmental quality and accessibility; thus, for similar reasons, urban planners tend to view compact, contiguous, connected, and mixed‐urban forms to have desirable features. Concern about the efficient configuration of other forms of urban infrastructure, such as wastewater services, schools, police, and fire, also tend to reinforce these preferences. But urban planners must balance concerns over the environment and accessibility against the concerns for social cohesion, equity, and property values. And there is little empirical evidence that these qualities are greater in communities that are compact, connected, and mixed. Whether or not all indicators favor compact, mixed‐use development, there is general agreement that local regulatory barriers to this type of development should be removed and more lifestyle choices should be made available to the changing population.

Research on sprawl at the street level, generally by urban designers, is shaped by principles of good urban form. Urban designers are trained to value coherence, imageability, transparency, etc. The evidence suggests that the general population values these features as well and that such features also tend to promote physical activity, personal safety, and perhaps social interaction. Perhaps the most important finding at this scale is that quality design can substitute for personal space and thus make high‐density development as, or even more, attractive than low‐density development. Public policies that achieve these results include form‐based codes and design review processes.

In sum, substantial work by researchers trained in various disciplines has made considerable progress measuring urban form and assessing its impacts on economic, social, and environmental factors. A large body of evidence suggests there are advantages to development that is dense and diverse. But in the abstract such normative principles of urban form have little meaning. To provide more concrete principles of urban form, Talen (2003) carefully describes and combines measures that correspond with the submetropolitan and community design scales of analysis. The present authors believe, however, that principles of urban form must consider landscape, metropolitan, and urban design perspectives as well. Only when these principles are applied at multiple scales and contexts do they have any real value for public policy.

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