Population density refers to the population of a particular area per square mile or square kilometer. For instance, on March 1, 1981, the population of India was estimated at 685.18 million, while the area was 3.29 million square kilometres, resulting in a density of 221 per square kilometer.
This is known as arithmetic density, a simple average which does not take into account either the clustering of people in large cities like Mumbai, Kolkata and Delhi, or the uninhabited desert of Ketch.
The arithmetic density is a crude measure and gives us a very broad picture of the actual situation; it does not take into: consideration the characteristics of the people or those of the areas which they inhabit.
The arithmetic density is particularly misleading for countries which have only a few centres of concentrated population, the rest of the area being virtually uninhabited.
A striking example of such a country is Egypt, where millions are crowded in the Nile Delta, while the rest of the country is very sparsely populated.
In order to overcome the weaknesses of the arithmetic density, it is advisable to compute it for the smallest possible unit, because the smaller the unit of measurement, the more meaningful will the arithmetic density be. The problem is that it is difficult to obtain the required information for smaller units.
The measure of arithmetical density may be refined by relating the total population, not to the entire territory of a country, but to only the cultivable land that is available. This is known as nutritional or physiological density.
The suitability of this measure may be illustrated by once again citing the example of Egypt, where the arithmetic density for the country is about 90 per square mile, while the physiological density is about 3,500 per square mile.
The limitation of this measure is that, while excluding all non- arable land from the denominator, it also excludes forests, wild pastures, mining land and scenic areas.
Moreover, it does not take into account the variations in the output of various arable lands because of differences in climate, soil and other characteristics.
“Still, it provides a better indicator than does the arithmetic density of the degree of crowding in a region compared with its physical potential for producing food and agricultural raw materials.
Japan’s arithmetic density in 1960, for example, was 655 per square mile; its nutritional density was an unbelievable 4,680, a fact which suggests the necessity for significant imports of food and vegetable raw materials.”
In the calculation on agricultural density, urban residents are excluded so that this measure gives a more or less accurate estimate of the pressure of population or rural areas.
It is especially useful for indicating population density in a more realistic way in regions in which farmers constitute a high proportion of the population. Settlement density represents the number of square miles/ kilometres in a country for each 100,000 persons or more.
“In the United Kingdom, there is a city for every 2,000 square miles, in the United States for 27,000 square miles, in China for 53,000 square miles.”
It is also possible to derive a country’s urban density, that is, the number of persons per sq. mile/kilometer of urban area, and its rural density, that is, the number of persons per sq. mile/kilometer of rural area or of land under cultivation.
The type data that are required for the calculation of such refined measure are, however, usually not available in most countries.