urban-rural gradient

Definition of "urban-rural gradient" as an ecological concept

"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." (from Baltimore Ecosystem Study Urban Lexicon,  http://besurbanlexicon.blogspot.com/2012/07/urban-rural-gradient.html)

Early expositions of this idea include:

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.

Another version from American Studies: Suburbs as Marriages of City and Country

Donaldson, Scott. 1968. "CITY AND COUNTRY: MARRIAGE PROPOSALS." American Quarterly 20, no. 3: 547-566.America: History & Life, EBSCOhost (accessed April 19, 2013).