30 July 2012


Definition: Urbanism refers to the body of knowledge about the organization, arrangement, and human functions of cities as well as the ways of life of city inhabitants.  Originally derived from the French word for city planning, it now also refers to a philosophy that recognizes the positive intellectual, social, and physical benefits of life in well functioning urban areas. 

Examples: Features of urbanism include 1) diversity of residents, in terms of age, ethnicity, and walks of life, 2) high density, favoring the potential for social contact and innovation, 3) availability of public transportation or arrangements that favor pedestrian access, 4) access to business, shops, entertainment, as well as work and school.  

Built over natural history of lower east side Manhattan. B. McGrath
Classic figure ground argument of the modern city of blocks in a "green space" of Le Corbusier's plan for St. Die and the traditional figure ground of Parma.
Why important: There are many models of urbanism, some of which emphasize the risks and vulnerabilities of urban living, and others which emphasize the benefits.  New urbanism, green urbanism, sustainable urbanism, and ecological urbanism are some of the models of urbanism in current circulation as ways to improve life in cities and suburbs.  Benefits extend to human quality of life and lowering environmental impact and conversion of wild or rural lands to human settlements.  Social and economic equity are also concerns of contemporary models of urbanism.

For more information:
·   Beatley, T. 2000. Green urbanism: learning from European cities. Island Press, Washington, DC.
·   Talen, E. 2005. New urbanism and American planning: the conflict of cultures. Routledge, New York.
·   McGrath, B. 1994. Transparent Cities. Lumen Books, Santa Fe.
·   Jacobs, J. 1961. The death and life of great American cities: the failure of town planning. Random House, New York.
·   Spirn, A.W. 1984. The granite garden: urban nature and human design. Basic Books, New York.

12 July 2012

Urban-rural Gradient

Definition: An ordering of sites based on the predominance of buildings and infrastructure, coupled with dense human population, in contrast with sites having sparse infrastructure and low human population density.  Other criteria, such as some physical or biological environmental measurement, such as pollution, or social contrasts such as dependence on an economy based on consumption, finance, transportation, versus dependence on agriculture or management of natural resources, can be used to contrast urban and rural sites. 

Examples: Urban-rural gradients can sometimes be found as continuous lines from an old downtown, through suburbs, and ending in forested or agricultural areas (Figure 1).  

Figure 1. The transect from the Bronx in New York  City to forested stands on the same bedrock in rural western Connecticut.  The transect was used to expose a gradient of adjacent land covers, road densities, and traffic volumes affecting forest stands (from McDonnell and Pickett 1990).  The quantification of the gradient in terms of the human variables is found in Medley, K. E., M. J. McDonnell, and S. T. A. Pickett. 1995. Forest-landscape structure along an urban-to-rural gradient. Professional Geographer 47:159-168.

Figure 2. The patchy distribution of pigeons at random sampling locations in Baltimore city.  The distribution is heterogeneous, but does not follow linear transects from the core of the city to the suburban edges of Baltimore.  C.H. Nilon & P.S. Warren.

Why important: Urban-rural gradients, both direct transects in space, and abstract comparisons based on quantitative or qualitative differences found in metropolitan areas, have become a widespread tool for research in urban socio-ecological systems.

For more information:
·        McDonnell, M. J. and S. T. A. Pickett. 1990. Ecosystem structure and function along urban-rural gradients: an unexploited opportunity for ecology. Ecology 71:1232-1237.
·      Hahs, A. K. and M. J. McDonnell. 2006. Selecting independent measures to quantify Melbourne's urban-rural gradient. Landscape and Urban Planning 78:435-448.
·      Clergeau, P., J. Jokimäki, and R. Snep. 2006. Using hierarchical levels for urban ecology. Trends in Ecology and Evolution 21:660-661.
·       Dow, K. 2000. Social dimensions of gradients in urban ecosystems. Urban Ecosystems 


Definition: A model is a representation of some place, process, or set of interactions.  A model may be physical, quantitative, or conceptual.  Models specify the boundaries of a system of interest in time and space, indicate what the components of the system are, and define how the components can interact with one another.  Finally, a model specifies the nature of the changes or any limits to change that the system can undergo.  Models are based on assumptions that reflect the choices of what is included and left out of the model, and how the relationships are structured. 

Examples: A map is a model of the spatial relationships deemed important in a spatial system.  Roadmaps, maps of historically important sites, or a depiction of subway stops are examples of maps as models.  Models may also exist in the form of equations such as those that describe the dynamics and limitations of biological populations or of interacting populations or predators and prey.  Models may be physical, as in the case of an architectural balsa wood and cardboard model of a building or neighborhood, or an experimental setup to examine how the conditions in a stream channel influence biological foodwebs.

Figure 1. An example of a conceptual model of interactions.  Based on the pulse-press model template for coupled natural-human systems (Collins et al. 2011), this specific example shows expected relationships between riparian structures and functions, ecosystem services, and human actions.  See Cadenasso et al. (2008) for further explanation of the relationships involved in this particular case.
δ φ/δt = D(δ2 φ/δx2)
Figure 2.  Fick’s second law of diffusion.  This model, in the form of an equation, describes the change in concentration (φ) of a substance over time (t). D = the diffusion coefficient and x is the position along the diffusion path.

Figure 3.  Brian McGrath (L) and Victoria Marshall (R), working with M.L. Cadenasso and Phanat Xanamane (not pictured) to construct a model of urban land cover integrating the cover and type of surfaces, vegetation, and buildings.  The resulting model has been called a “periodic table” of urban land cover.  See Cadenasso et al. (2007) for details of the components of the model.
Why important: All disciplines and practices use models.  However, how those models are used and constructed differs between disciplines.  In urban systems models range from the informal pictures of a neighborhood by its residents, to the policies employed by different levels of government or different jurisdictions.  Models of urban systems can emphasize the social, the economic, or environmental aspects of the metropolis, and may have different spatial limits.  Models can assume that the structures and processes within their boundaries are aggregated and uniform, or the models may account for the differences among institutional agents or spatial patches.  Many models of urban systems are beginning to treat them as complex systems capable of self organizations, in contrast to classical models of top down control by a narrow function, such as economy or law.

For more information
  • Band, L.E., C.L. Tague, S.E. Brun, D.E. Tennenbaum, and R.A. Fernandes. 2000. Modeling watersheds as spatial object hierarchies: structure and dynamics. Transactions in Geographic Information Systems 4 181-196.
  • Batty, M. 1995. New ways of looking at cities. Nature 377:574.
  • Shane, D.G. 2005. Recombinant urbanism: conceptual modeling in architecture, urban design, and city theory. John Wiley & Sons, Hoboken.
  • McGrath, B.P. 2008. Digital modelling for urban design. Wiley, London.
  • Cadenasso, M.L., S.T.A. Pickett, and K. Schwarz.  2007.  Spatial heterogeneity in urban ecosystems: Reconceptualizing land cover and a framework for classification. Frontiers in Ecology and Evolution 5: 80-88.
  • Kennedy, C., J. Cuddihy, and J. Engel-Yan. 2007. The changing metabolism of cities. Journal of Industrial Ecology 11:43-59.
  • Cadenasso, M.L., S.T.A. Pickett, P.M. Groffman, G.S. Brush, M.F. Galvin, J.M. Grove, G. Hagar, V. Marshall, B.P. McGrath, J. O’Neil-Dunne, W.P. Stack, A.R. Troy.  2008.  Exchanges across land-water-scape boundaries in urban systems: Strategies for reducing nitrate pollution.  Annals of the New York Academy of Sciences 1134: 213-232.
  • Collins, S. L., S. R. Carpenter, S. M. Swinton, D. E. Orenstein, D. L. Childers, T. L. Gragson, N. B. Grimm, J. M. Grove, S. L. Harlan, J. P. Kaye, A. K. Knapp, G. P. Kofinas, J. J. Magnuson, W. H. McDowell, J. M. Melack, L. A. Ogden, G. P. Robertson, M. D. Smith, and A. C. Whitmer. 2011. An integrated conceptual framework for long-term social-ecological research. Frontiers in Ecology and Environment 9:351-357.