Population of the world or of any country is not uniformly distributed. The same is true about India also. Some parts of the country are densely populated, some parts moderately populated and some parts are sparsely populated.
The size of population of different areas can be compared in many ways. One of the ways can be to compare the absolute size of the population. But it does not provide any idea about the relationship of population with the area or resource base of the country. This type of comparison is not adequate.
For example, population of Singapore is 4.2 million and that of Peoples Republic of China is 1,300 million. Indeed one is too small and the other is too big. Now take into consideration that the area of Singapore is just 630 sq km; whereas China has an area of 9.5 million sq km. This helps to know how crowded Singapore is as compared to China. Therefore, the population of various countries are generally compared in terms of density of population. This is a method of comparing the man-land ratio of different regions.
For this purpose, the population of a region is assumed to be distributed evenly in all its parts and the number of people per square kilometre is calculated. This is called arithmetic density of population which can be calculated by dividing the total population of a country or a region by the total area. Therefore, the density of population is expressed as the number of persons per square kilometre.
According to 2001 census, the density of population in India is 324 persons per square kilometre. Over the last 100 years density has increased more than four times. It has increased from 77 in 1901 to 324 in 2001. When we say that the density of population of India is 324 persons per square kilometre, this does not mean that population is exactly 324 persons in each and every square kilometre.
In reality, the distribution of population in India is highly uneven. The uneven density of population in India is clear from the fact that in Arunachal Pradesh the average number of population is only 13 persons per square kilometre, whereas it is 9,294 persons per square kilometre in Delhi as per 2001 census.