Population is the total count of people within a defined boundary. For example, the population of India is the total number of persons living within the borders of India. According to the United Nations, India's population in 2009 is 1,198,003,000 people.
Population density is the same concept as density of a material, in which density is the total mass divided by the volume. Population density is the total population in a bounded place divided by the land area of that place. For example, the CIA World Factbook shows that India has an area of 3,287,263 sq km, but only 2,973,193 sq km is land. The population density of India is then about 403 persons per square kilometer [(1,198,003,000 people)/(2,973,193 sq km)].
Any population density in a bounded place that is greater than the global average could be considered high population density. For example, India's population density is almost nine times that of the average across the earth (403/46=8.8) and can be considered a high population density.
Population density varies greatly across and within nations. For example, the population density of Canada is 3.6 persons per sq km (33,487,208 persons/9,093,507 sq km), which is not even one-one hundredth of India's population density. Toronto, Canada, however, has a high population density of 3,972 persons per sq km ( 2,503,281 persons/630.2 sq km).
Places with high population density can be a hotbed for disease and violence. Higher population densities, however, are considered the opposite of sprawling populations, and increasing population density in some areas might prevent conversion of agricultural land to urban uses.
