Population density is the ratio between number of peoples to the size of land. Density= population/area

On the basis of density world is divided into following regions :
1.Densely populated regions : In these regions there are 200 people per square kilometer on average. Ex- north eastern USA, east Asia etc.

2.low density regions : In these regions there is only 1 person per square kilometer. Ex- north and south poles, cold and hot deserts etc.

3.Medium density regions : There are 11 to 50 persons per square kilometer. Ex- Norway, Sweden, south India etc.

Reasons behind uneven density distribution of population are :
1.GEOGRAPHICAL FACTORS
(a) Availability of water
(b) Landforms : people prefer living on flat plains because such areas are favourable for crop production and making roads.
(c) Climate : areas with comfortable climate are favourable .
(d) Soils : fertile soils are important for agriculture.

2.ECONOMIC FACTORS
(a) Minerals - Areas with mineral deposits attract industries, mining, and generate employment.
(b) Urbanisation - cities offer better employment opportunities, educational and medical facilities better means of transportation etc.
(c) Industrialisation.

3.SOCIAL AND CULTURAL FACTORS
some places attract more people because they have religious or cultural significance.

Population density refers to the measurement of the number of individuals residing in a specific area or region. It is calculated by dividing the total number of people by the total land area of the region. Population density can be used to determine the level of pressure on resources and infrastructure in a particular region.

Classification of the world based on population density:

1. Highly dense regions:
These regions have a population density of over 500 people per square kilometer. Examples include cities such as Mumbai, Tokyo, and New York.

2. Moderately dense regions:
These regions have a population density ranging from 150 to 500 people per square kilometer. Examples include countries such as Bangladesh, Egypt, and the Philippines.

3. Sparsely populated regions:
These regions have a population density of less than 150 people per square kilometer. Examples include countries such as Australia, Canada, and Russia.

Reasons responsible for population density:

1. Urbanization:
Urbanization has led to the concentration of people in cities, resulting in high population density in urban areas.

2. Migration:
People tend to migrate to areas with better opportunities, leading to an increase in population density in those areas.

3. Fertility rates:
High fertility rates lead to an increase in the population, which can result in higher population density.

4. Land availability:
Areas with limited land availability tend to have a higher population density as people are forced to live in smaller areas.

5. Economic development:
Economically developed regions tend to have higher population density due to better opportunities and a higher standard of living.

In conclusion, population density is an important factor that can have significant impacts on a region's resources, infrastructure, and quality of life. Understanding the reasons behind population density can help policymakers make informed decisions about resource allocation and infrastructure development.