# Population density

Population density per square kilometre by country, 2006
Population density map of the world in 1994.

Population density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, humans in particular.

## Biological population densities

Population density is a common biological measurement and is often used by conservationists and measure than population size.

Low densities may cause an extinction vortex and lead to further reduced fertility. This is called the Allee effect, after W. C. Allee who first identified it. Examples of the causes in low population densities include:
• Increased problems with locating mates
• Increased inbreeding
Different species have different expected densities. R-selected species commonly have high population densities, while K-selected species may have lower densities. Low densities may be associated with specialised mate location adaptations such as specialised pollinators; as found in the orchid family (Orchidaceae).

The formula to calculate density is:

## Human population density

A street in Hong Kong, one of the most densely-populated places in the world.
A street in Ulan Bator, Mongolia - the least densely-populated country in the world.

For humans, population density is the number of people per unit of area (which may include or exclude cultivated or potentially productive area). Commonly this may be calculated for a county, city, country, another territory, or the entire world.

The world population is 6.6 billion humans, and Earth's area is 510 million square kilometers (200 million square miles). Therefore the world-wide human population density is 6.5 billion / 510 million = 13 per km² (33 per sq mi), or 43 per km² (112 per sq mi) considering that humans live on land, which forms 150 million km² (58 million sq mi) of the earth. This density rises with the population growth.

Several of the highest-density territories in the world are very large city-states, micronations or dependencies. These territories share a relatively small area and an exceptionally 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.

Cities with exceptionally high population densities are often considered to be overpopulated, though the extent to which this is the case depends on factors like quality of housing and infrastructure or access to resources. Most of the largest densely-populated cities are in southern and eastern Asia, though Cairo and Lagos in Africa also fall into the category. City population is however, heavily dependent on the definition used for the urban area: densities will be far higher for the central municipality than when more recently-developed and as yet administratively unincorporated suburbs are included, as in the concepts of agglomeration or metropolitan area, the latter including sometimes neighbouring cities.

## Other methods of measurement

While the arithmetic density is the most common way of measuring population density, several other methods have been developed which aim to provide a more accurate measure of population density over a specific area.
• Arithmetic density: The total number of people / area of land measured in km² or mi².
• Physiological density: The total population / the amount of arable land.
• Agricultural density: The total rural population / amount of agricultural land.
• Residential density : The number of people living in an urban area / the area of residential land.
• Urban density : The number of people inhabiting an urban area / the total area of urban land
• Ecological optimum: The density of population which can be supported by the area's natural resources.

population is the collection of people or organisms of a particular species living in a given geographic area or mortality, and migration, though the field encompasses many dimensions of population change including the family (marriage and divorce), public health, work and the
Plantae
• Chromalveolata
• Heterokontophyta
• Haptophyta
• Cryptophyta
• Alveolata

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Biological data is data or measurements collected from biological sources, which is stored or exchanged in a digital form. Biological data is commonly stored in files or databases. Examples of biological data are DNA base-pair sequences, and population data used in ecology.
The conservation movement is a political and social movement that seeks to protect natural resources including plant and animal species as well as their habitat for the future.
Extinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. Developed by M. E. Gilpin and M. E.
The Allee effect is a phenomenon in biology characterized by a positive correlation between population density and the per capita growth rate.

## Description

The Allee effect was first written on extensively by its namesake Warder Clyde Allee.
Warder Clyde Allee (June 5, 1885 - March 18, 1955) was an American zoologist and ecologist who taught animal ecology at the University of Chicago. He is best known for his research on animal behavior, protocooperation, and for identifying the Allee effect.
Inbreeding is breeding between close relatives, whether plant or animal. If practiced repeatedly, it often leads to a reduction in genetic diversity, and the increased gene expression of recessive traits, resulting in inbreeding depression.
In ecology, r/K selection theory relates to the selection of traits which promote success in particular environments. The theory originates from work on island biogeography by the ecologists Robert MacArthur and E. O. Wilson[1].
In ecology, r/K selection theory relates to the selection of traits which promote success in particular environments. The theory originates from work on island biogeography by the ecologists Robert MacArthur and E. O. Wilson[1].
Orchidaceae
Juss.

Subfamilies
• Apostasioideae
• Cypripedioideae
• Epidendroideae
• Orchidoideae
• Vanilloideae

Orchidaceae, also called the Orchid family, is the largest family of the flowering plants (Angiospermae).
List of countries and dependencies by population density in inhabitants/km². The list includes sovereign states and self-governing dependent territories that are recognized by the United Nations.
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A county is generally a sub-unit of regional self-government within a sovereign jurisdiction. Originally, in continental Europe, a county was the land under the jurisdiction of a count.
city is an urban settlement with a particularly important status which differentiates it from a town.

City is primarily used to designate an urban settlement with a large population. However, city may also indicate a special administrative, legal, or historical status.
In political geography and international politics, a country is a political division of a geographical entity, a sovereign territory, most commonly associated with the notions of state or nation and government.

Types of administrative and/or political territories include:

EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
world population is the total number of humans on Earth at a given time. In September 2007, the world's population is believed to have reached over 6.6 billion. In line with population projections, this figure continues to grow at rates that were unprecedented before the 20th
EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
A city-state is a region controlled exclusively by a city, usually having sovereignty. Historically, city-states have often been part of larger cultural areas, as in the city-states of ancient Greece (such as Athens, Sparta and Corinth), the Phoenician cities of Canaan (such as
Micronations — sometimes also referred to as cybernations, fantasy countries, model countries, and new country projects — are entities that resemble independent nations or states but which are unrecognized by world governments or major
country, state, and nation can have various meanings. Therefore, diverse lists of these entities are possible. Wikipedia offers the following lists:

Urbanization or Urbanisation (see difference in spelling) means the removal of the rural characteristics of a town or area, a process associated with the development of civilisation.
city is an urban settlement with a particularly important status which differentiates it from a town.

City is primarily used to designate an urban settlement with a large population. However, city may also indicate a special administrative, legal, or historical status.
Overpopulation is a condition when an organism's numbers exceed the carrying capacity of its ecological niche. In common parlance, the term usually refers to the relationship between the human population and its environment, the Earth.
Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area (or 29.4% of its land area) and, with almost 4 billion people, it contains more than 60% of the world's current human population.
Cairo
القـــاهـــر?

Flag
Seal
Egypt: Site of Cairo (top center)
Coordinates:
Government