Shrinking cities are dense cities that have experienced notable population loss. Out-migration is a common reason that cities shrink. Since the infrastructure of such cities was built to support a larger population, its maintenance can become a serious concern. A related phenomenon is counter urbanization.
Global context 
The current population of the world is 7.0 billion people. Currently about 3 billion live in cities. By 2030, population in cities is expected to be 4.1 billion. Though some cities are continuing to attract residents, others are losing residents at varying rates.[vague] Saskia Sassen's "global cities" theory forecasts these urban "winners" and "losers": the winners being those cities with agglomerated financial and specialized services and the losers being those with outdated industrial infrastructure and manufacturing economies.
In the last 50 years, about 370 municipalities with more than 100,000 residents have undergone population losses of more than 10%. More than 25 percent of the depopulating cities are in the United States, and most of those are in the midwest. Shrinking cities at the metropolitan area level or the urban area level are far less frequently occurring.
According to a German poster, the countries with the largest numbers of shrinking cities are the United States (59), China (33), the United Kingdom (27), Germany (26), Brazil (23), Italy (22), Ukraine (17), South Africa (17), Nigeria (14), Kazakhstan (13), Russia (13), Japan (12), Chile (10), India (9), Vietnam (9), and Indonesia (8).
Problems with Infrastructure Management 
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Among many challenges facing shrinking cities, infrastructure management is among the most intractable. Shrinking cities were once more dense, and have vast infrastructure to support economic activity. However, they now face a reduced population. The remaining infrastructure was intended for a larger population.
Overcapacity may strain the fiscal situation. The problem is relatively straightforward; a city has a higher per capita cost to the residents who remain. Where infrastructure costs are fixed, reductions in demand may strain budgets.
The dispersed neighborhoods that inevitably characterize shrinking cities are a major source of fiscal distress. Services must still be provided to fewer and fewer citizens over a larger geographic distance, once again raising the per capita cost. This is an instance illustrating how a lack of population density can be a strain on already stretched municipal budgets. “At the neighbourhood level, residential density is directly linked to expenditures on neighbourhood infrastructure. The higher the density, the lower the per capita length of collector roads, water distribution lines or sewer collection lines. Below a density of 40 dwellings per hectare net urban land network-related per capita costs increase exponentially”.
Some policymakers have suggested that such neighborhoods might be consolidated at a higher density to increase their ability to pay for the required municipal services. Decommissioning public infrastructure is an elaborate, expensive process that requires a great deal of study. Currently, many infrastructure management professionals believe it more sensible to incur current maintenance cost at some minimal level rather than removing infrastructure that may later need to be reinstated.
Detailed research regarding infrastructure management in shrinking cities is not widespread at this point. Kent State University’s Sustainable Infrastructure in Shrinking Cities report consistently affirms this point. Simply put, far more research is needed before we can confidently recommend policy. As the report concludes:
“When we began this research, we hoped to find a technology or strategy that would enable substantial cost savings by decommissioning large components of costly infrastructure that were no longer necessary due to declining population. We found no such thing.”
Several approaches are being employed in various cities to attempt to address the problem, using a combination of financial incentives and regulatory controls.
Revitalization of core areas to make them more attractive to businesses and residents have had some positive results.
An urban growth boundary is an attempt to limit sprawl, which necessarily increases density within the boundary. Its intent is to prevent the problem of urban shrinkage before it happens. The boundary generally encompasses the city and its surrounding suburbs, requiring the entire area to work together to prevent urban shrinkage. This method is being used successfully in many cities (such as Portland, Oregon) to maximize returns on infrastructure investments.
Artistic approaches to remediation include examples such as Lily Yeh's work at the Village of Arts and Humanities in North Philadelphia.
See also 
- Largest cities in the United States by population by decade
- Shrinking cities in the USA
- List of Canadian municipalities having experienced population decreases
General references 
- Hollander, Justin B. (forthcoming, 2011). Sunburnt Cities: The Great Recession, Depopulation, and Urban Planning in the American Sunbelt. London/New York: Routledge.
- Schiller, G (2007). Demographic Change and Infrastructural Cost – A Calculation Tool for Regional Planning. Paper proposed for SUE-MoT Conference 2007, Glasgow “Economics of Urban Sustainability”, Leibniz Institute of Ecological and Regional Development. Retrieved from http://download.sue-mot.org/Conference-2007/Papers/Schiller.pdf
- Sassen, Saskia (2000) Cities in a World Economy. Thousand Oaks, CA: Sage.
- , Metro Times - Arts: Detroit is not alone
- Hoornbeek, J (2009). Literature Review. Sustainable Infrastructure in Shrinking Cities, Kent State University, Center for Public Administration and Public Policy and the Cleveland Urban Design Collaborative. Retrieved from http://www.scribd.com/doc/54064004/Sustainable-Infrastructure-in-Shrinking-Cities
- COST-Action: CIRES (Cities Regrowing Smaller)
- SCiRN™ (The Shrinking Cities International Research Network)
- Shrinking Cities Exhibition
- Shrinking Cities in USA
- Interview with German expert Wolfgang Kil on Shrinking Cities in Germany
- Professor Hollander's research on shrinking cities
- Small, Green, and Good: The Role of Neglected Cities in a Sustainable Future, a Boston Review article which argues that shrinking cities can be revived in a future concerned with environmentalism, in particular by using urban agriculture to provide local food sources
- Shrinking Cities Institute
- The Village of Arts and Humanities