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Population density can be used as a measurement of any tangible item. However it is most frequently applied to living organisms. Population density is usually expressed in terms of items or organisms per unit area.
Note that population density, according to this definition, depends on the scale of the sampling area used, and is hard to define as a real-valued continuous function over the area in question. If the items concerned are modelled as discrete points, the population density will jump up and down as the edge of the sampling area passes over individuals. Modelling the individuals as spatially extended objects has other problems, as the scale of the sampling area approaches the scale of an object (for example, a person's scale may be regarded as the size of the grounds of their dwelling place: for some people, this will be a large area).
To resolve some of these problems, population density may be regarded, like coastline distance, as a scale-dependent fractal quantity.
Population density is a common biological measurement and is often used by conservationists as a more appropriate measure than absolute numbers. Low population densities may cause an extinction vortex , where low densities lead to further reduced fertility. This is referred to as the Allee effect , named after W. C. Allee , who first identified it. Examples of this may include;
However it should be noted that different species will have different expected densities. For example r selected species commonly have high population densities, while k selected species may have lower population densities. Low population densities may be associated with specialised mate location adaptations such as specialised pollinators, as is found in the orchid family, (the Orchidaceae.)
For human beings, population density is the number of persons per unit of area (which may include or exclude inland water), though it may also be expressed in relation to habitable, inhabited, productive (or potentially productive) or cultivated area.
It is frequently measured in persons per square mile or persons per square kilometre or hectare, which can be obtained simply by dividing the number of persons by the land area measured in square miles or in square kilometers or hectares.
Commonly this may be calculated for a county, city, country or the entire world. In the country articles the density is based on land area. However, the list of countries by population density is based on total area, including inland water.
Countries or territories with the highest population densities are:
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.
The most densely populated large state is BangladeshThe People's Republic of Bangladesh is a country in South Asia that forms the eastern part of the ancient region of Bengal. Bangladesh literally means "The Country of Bengal". Lying north of the Bay of Bengal, on land it borders India almost exclusively,, where 134 million people live in a highly agricultural area around the lower Ganges river, with a national population density in excess of 900 persons per km˛. World overall population density presently averages 42 persons per km˛.
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 AsiaThe continent of Asia is defined by subtracting Europe and Africa from the great land mass of Africa-Eurasia. The boundaries are vague, especially between Asia and Europe: Asia and Africa meet somewhere near the Suez Canal. The boundary between Asia and E, though CairoCairo ( Arabic: ; romanized: al-Qāhirah is the capital city of Egypt and has an estimated metropolitan area population of 15 million. It is the largest city in both Africa and the Middle East and is currently the thirteenth most populous city in the and LagosAlternate uses: Lagos (disambiguation Lagos is the largest city in Nigeria and, with its population of 13. 4 million ( 2000), one of the largest in Africa (second only to Cairo, Egypt). Lagos was the capital of Nigeria until 1991 when the capital was move in AfricaAfrica is the world's second-largest continent in both area and population, after Asia. 30,244,050 km2 (11,677,240 mi2) including the islands, it covers 20. 3% of the total land area on Earth, and with over 800 million human inhabitants it accounts for ar 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 agglomerationIn the study of human settlements, an agglomeration is an extended city or town area comprising the built-up area of a central place (usually a municipality) and any suburbs or adjacent satellite towns. Conurbation is a more specific term for urban cluste or metropolitan areaA metropolitan area is a large population center consisting of a large city and its adjacent zone of influence, or of several neighboring cities or towns and adjoining areas, with one or more large cities serving as its hub or hubs. A metropolitan area us, the latter including sometimes neighbouring cities.
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