Population density

Population density is population divided by total land area, sometimes including seas and oceans, as appropriate.

Low densities may cause an extinction vortex and further reduce fertility. This is called the Allee effect after the scientist who identified it. Examples of the causes of reduced fertility in low population densities are:[http://www.eoearth.org/article/Minimum_viable_population_size Minimum viable population size]. {{Webarchive|url=https://web.archive.org/web/20121006221151/http://www.eoearth.org/article/Minimum_viable_population_size |date=October 6, 2012 }} Eoearth.org (March 6, 2010). Retrieved on December 10, 2011.

• Increased problems with locating sexual mates
• Increased inbreeding

===Human densities===

{{Main|List of countries and dependencies by population density}}

File:World Population Density Map 2020.png

Population density is the number of people per unit of area, usually transcribed as "per square kilometre" or square mile, and which may include or exclude, for example, areas of water or glaciers. Commonly this is calculated for a county, city, country, another territory or the entire world.

World population is around 8,000,000,000[https://www.census.gov/popclock/ U.S. & World Population Clocks] and the Earth's total area (including land and water) is {{cvt|510,000,000|km2}}.[https://www.cia.gov/the-world-factbook/countries/world/ World]. CIA World Factbook Therefore, the worldwide human population density is approximately 8,000,000,000 ÷ 510,000,000 = {{cvt|16|/km2}}. However, if only the Earth's land area of {{cvt|150,000,000|km2}} is taken into account, then human population density is {{cvt|53|/km2}}. This includes all continental and island land area, including Antarctica. However, if Antarctica is excluded, then population density rises to over {{convert|58|/km2}}. File:vegetation.png

The European Commission's Joint Research Centre (JRC) has developed a suite of (open and free) data and tools named the Global Human Settlement Layer (GHSL) to improve the science for policy support to the European Commission Directorate Generals and Services and as support to the United Nations system.{{Cite journal|title=The global human settlement layer sets a new standard for global urban data reporting with the urban centre database |journal=Frontiers in Environmental Science |date=2022-09-15 | doi=10.3389/fenvs.2022.1003862 | doi-access=free | last1=Melchiorri | first1=Michele | volume=10 }}

Several of the most densely populated territories in the world are city-states, microstates and urban dependencies.{{cite web| url=https://www.un.org/esa/population/publications/wpp2008/wpp2008_text_tables.pdf | title=World Population Prospects, Table A.1| version=2008 revision | publisher=United Nations | author=Department of Economic and Social Affairs Population Division | year=2009 | access-date= March 12, 2009}}{{efn|The Monaco government uses a smaller surface area figure resulting in a population density of {{cvt|18,078|/km2}}.}} In fact, 95% of the world's population is concentrated on just 10% of the world's land.{{Cite web|title=Urbanization: 95% Of The World's Population Lives On 10% Of The Land|url=https://www.sciencedaily.com/releases/2008/12/081217192745.htm|access-date=2020-09-01|website=ScienceDaily|language=en}} These territories have a relatively small area and a high urbanization level, with an economically specialized city population drawing also on rural resources outside the area, illustrating the difference between high population density and overpopulation.

Deserts have very limited potential for growing crops as there is not enough rain to support them. Thus, their population density is generally low. However, some cities in the Middle East, such as Dubai, have been increasing in population and infrastructure growth at a fast pace.{{Cite book|title=Desert regions : population, migration, and environment |last1=Portnov |first1=B. A. |last2=Hare |first2=A. Paul |date=1999|publisher=Springer|isbn=3540657800|oclc=41320143}}File:Mongolian Steppes (6228096139).jpg is the least densely populated country in the world due to its harsh climate as a result of its geography.{{cite web|url=https://www.sidmartinbio.org/why-mongolia-is-sparsely-populated/|title=Why Mongolia is sparsely populated?|work=Esther Fleming|publisher=SidmartinBio}}]]Cities with high population densities are, by some, considered to be overpopulated, though this will depend on factors like quality of housing and infrastructure and access to resources.[http://www.globalissues.org/issue/198/human-population Human Population]. Global Issues. Retrieved on December 10, 2011. Very densely populated cities are mostly in Asia (particularly Southeast Asia); Africa's Lagos, Kinshasa, and Cairo; South America's Bogotá, Lima, and São Paulo; and Mexico City and Saint Petersburg also fall into this category.[http://www.citymayors.com/statistics/largest-cities-density-125.html The largest cities in the world by land area, population and density] {{Webarchive|url=https://web.archive.org/web/20150516053854/http://www.citymayors.com/statistics/largest-cities-density-125.html |date=May 16, 2015 }}. Citymayors.com. Retrieved on December 10, 2011.File:Monaco by night.JPG is currently the most densely populated nation in Europe.]]City population and especially area are, however, heavily dependent on the definition of "urban area" used: densities are almost invariably higher for the center only than when suburban settlements and intervening rural areas are included, as in the agglomeration or metropolitan area (the latter sometimes including neighboring cities).

In comparison, based on a world population of 8 billion, the world's inhabitants, if conceptualized as a loose crowd occupying just under {{cvt|1|m2|-1}} per person (cf. Jacobs Method), would occupy an area of {{convert|8000|km2|sqmi}} a little less than the land area of Puerto Rico, {{convert|8868|km2|sqmi}}.

{{main|List of countries and dependencies by population density}}

File:EU Pop2008 1024.PNG of the European Union (2007–2012) uses areas and colors to represent population.]]

File:Living population density.png

Although the arithmetic density is the most common way of measuring population density, several other methods have been developed to provide alternative measures of population density over a specific area.

• Arithmetic density: The total number of people / area of land
• Physiological density: The total population / area of arable land
• Agricultural density: The total rural population / area of arable land
• Residential density: The number of people living in an urban area / area of residential land
• Urban density: The number of people inhabiting an urban area / total area of urban land
• Ecological optimum: The density of population that can be supported by the natural resources
• Population weighted density: Also known as living density, population density at which the average person lives[https://gmnenad.com/2021/05/analysis-of-real-population-density-per-countries/ Analysis of living population density per countries], based on NASA SEDAC world gridded data.

• Distance sampling
• Demography
• Human geography
• Idealised population
• List of population concern organizations
• Population dynamics
• Population decline
• Population growth
• Population genetics
• Population health
• Population momentum
• Population pyramid
• Rural transport problem
• Significant figures
• Small population size

• List of Australian suburbs by population density
• List of countries by population density
• List of cities by population density
• List of city districts by population density
• List of English districts by population density
• List of European Union cities proper by population density
• List of islands by population density
• List of states and territories of the United States by population density

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• [http://www.demographia.com/db-citydenshist.htm Selected Current and Historic City, Ward & Neighborhood Density]
• {{cite web |url= http://luminocity3d.org/WorldPopDen |title= World Population Density |author= Duncan Smith / UCL Centre for Advanced Spatial Analysis |quote= exploratory map shows data from the [...] Global Human Settlement Layer (GHSL) produced by the European Commission JRC and the CIESIN Columbia University}}

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