Urban density is a term used in urban planning and urban design to refer to the number of people inhabiting a given urbanized area. As such it is to be distinguished from other measures of population density. Urban density is considered an important factor in understanding how cities function. Research related to urban density occurs across diverse areas, including economics, health, innovation, psychology and geography as well as sustainability.
A 2019 meta-analysis of 180 studies on a vast number of economic outcomes of urban density concluded that urban density had net positive effects but had some regressive distributional effects, which is to say, a negative impact on lower-income residents.
It is commonly asserted that higher density cities are more sustainable than low density cities. Much urban planning theory, particularly in North America, the UK, Australia and New Zealand has been developed premised on raising urban densities, such as New Urbanism, transit-oriented development, and smart growth. This assertion, however, remains a contested or challenged one.
The link between urban density and aspects of sustainability remains a contested area of planning theory. Jan Gehl, prominent Urban Designer and expert on sustainable urbanism, argues that low-density, dispersed cities are unsustainable as they are automobile dependent. NASA, for example, has established a direct correlation between urban density and air pollution.
Others, such as Randy O'Toole of the Libertarian Cato Institute, point to how raising densities results in more expensive real estate, greater road congestion and more localized air pollution. At a broader level, there is evidence to indicate a strong negative correlation between the total energy consumption of a city and its overall urban density, i.e. the lower the density, the more energy consumed.
Urban density is a very specific measurement of the population of an urbanized area, excluding non-urban land-uses. Non-urban uses include regional open space, agriculture and water-bodies.
There are a variety of other ways of measuring the density of urban areas:
- Floor area ratio - the total floor area of buildings divided by land area of the lot upon which the buildings are built
- Residential density - the number of dwelling units in any given area
- Population density - the number of human persons in any given area
- Employment density - the number of jobs in any given area
- Gross density - any density figure for a given area of land that includes uses not necessarily directly relevant to the figure (usually roads and other transport infrastructure)
- Net density - a density figure for a given area of land that excludes land not directly related to the figure.
- Weighted density - a density metric which measures the density at which the average citizen lives. It is determined by calculating the standard density of each census tract, assigning each a weight equal to its share of the total population, and then adding the segments.
- Ahlfeldt, Gabriel M.; Pietrostefani, Elisabetta (2019). "The economic effects of density: A synthesis". Journal of Urban Economics. 111: 93–107. doi:10.1016/j.jue.2019.04.006.
- Williams, Katie, Elizabeth Burton, and Mike Jenks. "Achieving the compact city through intensification: An acceptable option." The compact city: A sustainable urban form (1996): 83-96.
- Jones, Christopher (2014). "Spatial Distribution of U.S. Household Carbon Footprints Reveals Suburbanization Undermines Greenhouse Gas Benefits of Urban Population Density". Environmental Science and Technology. 48 (2): 895–902. doi:10.1021/es4034364. PMID 24328208.
- "NASA scientists relate urban population to air pollution". NASA's Earth Science News Team. 2013. doi:10.1016/j.jul.2019.08.006 (inactive 2019-08-20). Retrieved 2019-07-09.
- Newman, Peter; Jeffrey R. Kenworthy (1999). Sustainability and Cities: Overcoming Automobile Dependence. Island Press. ISBN 978-1-55963-660-5.
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- Pont, Meta Y. Berghauser and Haupt, Per (2010) Spacematrix: Space, Density and Urban Form, NAi Publishers, ISBN 9789056627423
- Dovey, Kim and Pafka, Elek (2014) "The urban density assemblage: Modelling multiple measures" in Urban Design International, vol.19, nr. 1, pg.66-76