Editing Megacity (section)

==Challenges==
{{Cleanup|section|reason=A lot of vague statements without up-to-date / worldwide-applicable supporting examples or data. Can also be further expanded.|date=May 2014}}

===Slums===
[[File:Mumbai (5356346073).jpg|thumb|[[Mumbai]]'s [[Dharavi]] slum is home to 1 million residents]]
According to the United Nations, the proportion of urban dwellers living in [[slum]]s or informal settlements decreased from 47 percent to 37 percent in the [[developing world]] between 1990 and 2005.<ref>{{cite web|url=http://www.un.org/millenniumgoals/pdf/mdg2007.pdf |title=p. 26 |access-date=2010-09-01}}</ref> However, due to rising population, the absolute number of slum dwellers is rising and passed 1 billion in 2018.<ref>{{cite web | url=https://unstats.un.org/sdgs/report/2019/goal-11/ | title=— SDG Indicators }}</ref> The increase in informal settlement population has been caused by massive migration, both internal and transnational, into cities, which has caused growth rates of urban populations and spatial concentrations not seen before in history.{{Citation needed|date=May 2014}} The majority of these are located in informal settlements which often lack sufficient quality housing, sanitation, drainage, water access, and officially recognized addresses. These issues raise problems in the political, social, and economic arenas.<ref>{{cite web | url=https://www.weforum.org/stories/2023/08/informal-settlements-are-growing-heres-how-we-provide-everyone-a/ | title=Informal settlements are growing everywhere — here's what we do }}</ref> People who live in slums or informal settlements often have minimal or no access to education, healthcare, or the urban economy.

===Crime===
[[File:View over Complexo do Alemao (Favela) - From Igreja da Penha - Rio de Janeiro - Brazil - 03 (17556920491).jpg|thumb|Most murders in [[Rio de Janeiro]], Brazil are [[gang]] related and happen in the [[favela]]s]]
As with any large concentration of people, there is usually crime.<ref>{{cite journal |last1=Glaeser |first1=Edward L. |last2=Sacerdote |first2=Bruce |title=Why is There More Crime in Cities? |journal=[[Journal of Political Economy]] |date=1999 |volume=107 |issue=S6 |pages=S225–S258 |doi=10.1086/250109|s2cid=56443047 |url=http://papers.nber.org/papers/w5430.pdf }}</ref><ref>{{cite journal |last1=Yang |first1=V. Chuqiao |last2=Papachristos |first2=Andrew V. |last3=Abrams |first3=Daniel M. |title=Modeling the origin of urban-output scaling laws |journal=[[Physical Review E]] |date=2019 |volume=100 |issue=3 |pages=032306 |doi=10.1103/PhysRevE.100.032306|pmid=31639910 |arxiv=1712.00476 |bibcode=2019PhRvE.100c2306Y |s2cid=201646296 }}</ref> High population densities often result in higher crime rates, as visibly seen in growing megacities such as [[Organised crime in Pakistan|Karachi]], [[Crime in India|Delhi]], [[Crime in Egypt|Cairo]], [[Crime in Brazil|Rio de Janeiro]], and [[Crime in Nigeria|Lagos]].<ref>{{cite book|url=https://books.google.com/books?id=F9mHmudq2scC |title=The Real Population Bomb: Megacities, Global Security & the Map of the Future |author1=P. H. Liotta |author2=James F. Miskel |publisher=Potomac Books |date= 2012-02-01|access-date=2014-05-03|isbn=9781597975513 }}</ref>

===Homelessness===

Megacities often have significant numbers of [[Homelessness|homeless]] people. The actual legal definition of homelessness varies from country to country, or among different entities or institutions in the same country or region.<ref>{{cite web|url=http://www.homeless.org.au/glossary.htm |title=Glossary defining homelessness |publisher=Homeless.org.au |access-date=2010-09-01}}</ref>

In 2002, research showed that children and families were the largest growing segment of the homeless population in the United States,<ref>FACS, "Homeless Children, Poverty, Faith and Community: Understanding and Reporting the Local Story", March 26, 2002
Akron, Ohio. {{cite web |url=http://www.facsnet.org/edu/progs/family_03-26-02.php3 |title=Homeless Children, Poverty, Faith and Community: Understanding and Reporting the Local Story |access-date=2006-10-24 |url-status=dead |archive-url=https://web.archive.org/web/20070928072235/http://www.facsnet.org/edu/progs/family_03-26-02.php3 |archive-date=2007-09-28 }}</ref><ref>National Coalition for the Homeless, "Homeless Youth" 2005 {{cite web|url=http://www.nationalhomeless.org/publications/facts/youth.pdf|title=Homeless Youth|access-date=2013-04-15|archive-date=2018-08-22|archive-url=https://web.archive.org/web/20180822050017/http://www.nationalhomeless.org/publications/facts/youth.pdf|url-status=dead}}&nbsp;{{small|(164&nbsp;KB)}}</ref> and this has presented new challenges, especially in services, to agencies.<!-- Too specific? Applies worldwide. --> In the US, the government asked many major cities to come up with a ten-year plan to end homelessness. One of the results of this was a "[[Housing first]]" solution, rather than to have a homeless person remain in an emergency homeless shelter it was thought to be better to quickly get the person permanent housing of some sort and the necessary support services to sustain a new home. But there are many complications with this kind of program and these must be dealt with to make such an initiative work successfully in the middle to long term.<ref name="HF1">Abel, David, [http://www.boston.com/news/local/articles/2008/02/24/for_the_homeless_keys_to_a_home/ "For the homeless, keys to a home: Large-scale effort to keep many off street faces hurdles"], Boston Globe, February 24, 2008.</ref><ref name="HF2">[[Public Broadcasting Service|PBS]], [https://www.pbs.org/now/shows/305/index.html "Home at Last?&nbsp;– A radical new approach to helping the homeless"], ''[[NOW on PBS|NOW]]'' TV program, December 21, 2007.</ref>

===Traffic congestion===
[[File:Ratchadamri to Pratunam.jpg|thumb|[[Bangkok]] is notorious for its traffic congestion.]]

[[Traffic congestion]] is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, increased pollution, and increased vehicular [[Queueing theory|queueing]]. The [[Texas Transportation Institute]] estimated that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 5.7 billion U.S. gallons (21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity, or about 0.7% of the nation's [[Gross domestic product|GDP]]. It also estimated that the annual cost of congestion for each driver was approximately $1,000 in very large cities and $200 in small cities.<ref>{{Cite book |last=Sabry |first=Fouad |url=https://books.google.com/books?id=5r3-EAAAQBAJ&dq=congestion+$1,000++$200&pg=PT145 |title=Induced Demand: Unlocking the Mysteries of Induced Demand, Navigating the Roads to Sustainable Cities |date=2024-03-27 |publisher=One Billion Knowledgeable |language=en}}</ref> Traffic congestion is increasing in major cities and delays are becoming more frequent in smaller cities and rural areas. It also can result in various issues, including economic losses, energy waste, air and noise pollution, and more.<ref name=":0" />

===Urban sprawl===
[[File:South-Los-Angeles-110-and-105-freeways-Aerial-view-from-north-August-2014.jpg|thumb|right|A flat land area in the [[Greater Los Angeles Area]] in the U.S. state of California with houses, buildings, roads, and freeways. Areas constructed to capacity contribute to [[urban expansion]].]]

[[Urban sprawl]], also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its [[suburb]]s to its outskirts to low-density, auto-dependent development on rural land, with associated design features that encourage [[car dependency]].<ref name="sprawlcity">{{usurped|1=[https://web.archive.org/web/20100105123334/http://www.sprawlcity.org/hbis/wis.html What is Sprawl?]}}. ''SprawlCity.org''. Retrieved on 2008-02-07.</ref> As a result, some critics argue that sprawl has certain disadvantages including longer transport distances to work, high [[Automobile dependency|car dependence]], inadequate facilities (e.g. health, cultural. etc.) and higher per-person infrastructure costs. Discussions and debates about sprawl are often obfuscated by the ambiguity associated with the phrase. For example, some commentators measure sprawl only with the average number of residential units per acre in a given area. But others associate it with decentralization (spread of population without a well-defined center), discontinuity (leapfrog development), segregation of uses, etc.<ref>{{Cite book |last=Jain |first=Shri V. K. |url=https://books.google.com/books?id=qRYsEAAAQBAJ&dq=sprawl+decentralization+discontinuity++segregation&pg=PA352 |title=Applied Ecology and Sustainable Environment |date=2021-04-30 |publisher=BFC Publications |isbn=978-93-90880-19-5 |language=en}}</ref>

===Gentrification===
[[Gentrification]] and urban gentrification are terms for the socio-cultural changes in an area as a result of wealthier people buying property in a less prosperous community.<ref name="PBS">{{cite web|url=https://www.pbs.org/pov/flagwars/special_gentrification.php|title=PBS Documentaries with a point of view: What is Gentrification?|author=Benjamin Grant|publisher=Public Broadcasting Service|date=June 17, 2003|access-date=September 4, 2017|archive-date=December 6, 2015|archive-url=https://web.archive.org/web/20151206002239/http://www.pbs.org/pov/flagwars/special_gentrification.php|url-status=dead}}</ref> As living costs rise, lower-income residents are forced to move out of the community leading to an increase in average income, which in turn makes the area more desirable to other wealthier property or business owners, further pushing the living costs up. This process also tends to lead to a decrease in average family size in the area. This type of population change reduces industrial [[land use]] when it is redeveloped for commerce and housing.

===Air pollution===
[[File:Shanghai Smog.JPG|thumb|Air pollution in [[Shanghai]], China]]
[[Air pollution]] is the introduction into the [[Earth's atmosphere|atmosphere]] of [[chemical]]s, [[Atmospheric particulate matter|particulate matter]], or [[biotic material|biological materials]] that cause harm or discomfort to humans or other living organisms, or damages the [[natural environment]].<ref>{{cite journal |last1=Decker |first1=Ethan H. |last2=Elliott |first2=Scott |last3=Smith |first3=Felisa A. |title=Megacities and the Environment |journal=[[The Scientific World Journal]] |date=2002 |volume=2 |pages=374–386 |doi=10.1100/tsw.2002.103|pmid=12806023 |pmc=6009397 |doi-access=free }}</ref><ref>{{cite journal |last1=Folberth |first1=Gerd A. |last2=Butler |first2=Timothy M. |last3=Collins |first3=William J. |last4=Rumbold |first4=Steven T. |title=Megacities and climate change – A brief overview |journal=[[Environmental Pollution (journal)|Environmental Pollution]] |date=2015 |volume=203 |pages=235–242 |doi=10.1016/j.envpol.2014.09.004 |pmid=25300966 |doi-access=free|bibcode=2015EPoll.203..235F }}</ref> This issue is particularly prevalent in developing nations. As part of the Global Environment Monitoring System, [[WHO]] and [[UNEP]] established an air pollution monitoring network that oversees 50 cities.<ref>{{Cite journal |last1=Mage |first1=David |last2=Ozolins |first2=Guntis |last3=Peterson |first3=Peter |last4=Webster |first4=Anthony |last5=Orthofer |first5=Rudi |last6=Vandeweerd |first6=Veerle |last7=Gwynne |first7=Michael |date=1996-03-01 |title=Urban air pollution in megacities of the world |url=https://linkinghub.elsevier.com/retrieve/pii/1352231095002197 |journal=Atmospheric Environment |series=Supercities: Environment Quality and Sustainable Development |volume=30 |issue=5 |pages=681–686 |doi=10.1016/1352-2310(95)00219-7 |bibcode=1996AtmEn..30..681M |issn=1352-2310}}</ref> Many urban areas have significant problems with [[smog]], a type of [[air pollution]] derived from [[Motor vehicle emissions|vehicle emissions]] from [[internal combustion engine]]s and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form [[photochemical smog]].<ref name=":0" />

===Energy and material resources===
The sheer size and complexity of megacities gives rise to enormous social and environmental challenges. Whether megacities can develop sustainably depends to a large extent on how they obtain, share, and manage their energy and material resources. There are correlations between [[Electric energy consumption|electricity consumption]], heating and industrial fuel use, [[ground transportation]] energy use, [[Drinking water|water consumption]], [[Waste|waste generation]], and [[Steel making|steel production]] in terms of level of consumption and how efficiently they use resources.<ref>{{cite journal |last1=Kennedy |first1=Christopher A. |last2=Stewart |first2=Iain |last3=Facchini |first3=Angelo |last4=Cersosimo |first4=Igor |last5=Mele |first5=Renata |last6=Chen |first6=Bin |last7=Uda |first7=Mariko |last8=Kansal |first8=Arun |last9=Chiu |first9=Anthony |last10=Kim |first10=Kwi-gon |last11=Dubeux |first11=Carolina |last12=Lebre La Rovere |first12=Emilio |last13=Cunha |first13=Bruno |last14=Pincetl |first14=Stephanie |last15=Keirstead |first15=James |last16=Barles |first16=Sabine |last17=Pusaka |first17=Semerdanta |last18=Gunawan |first18=Juniati |last19=Adegbile |first19=Michael |last20=Nazariha |first20=Mehrdad |last21=Hoque |first21=Shamsul |last22=Marcotullio |first22=Peter J. |last23=González Otharán |first23=Florencia |last24=Genena |first24=Tarek |last25=Ibrahim |first25=Nadine |last26=Farooqui |first26=Rizwan |last27=Cervantes |first27=Gemma |last28=Sahin |first28=Ahmet Duran |title=Energy and material flows of megacities |journal=Proceedings of the National Academy of Sciences |date=2015 |volume=112 |issue=19 |pages=5985–5990 |doi=10.1073/pnas.1504315112 |pmid=25918371 |pmc=4434724 |bibcode=2015PNAS..112.5985K |doi-access=free}}</ref>