Wide variations in the density of population are mainly due to physical, cultural and human factors.
(a) Physical factors:
Places having favorable environmental conditions are more densely populated than the places having an adverse climate, mountainous and hilly regions have low density of population, where as, lowlands, river valleys and coastal plains are densely populated.
Climate Areas receiving heavy rainfall (equatorial regions) or scanty rainfall (cold polar region and deserts) are sparsely populated. Regions with adequate rainfall and fertile soil are densely populated. Tropical and mid-latitude regions are more densely populated than the rain forests and deserts. On the other hand interiors of the continents where rainfall is inadequate, have a low density, and rearing of animals is the main occupation. A large area is needed for grazing the animals.
(b) Cultural Factors:
Mode of life of the people affect the distribution of population. For example, areas with primitive people practicing food gathering, hunting, fishing, pastoral Nomadism, etc have a low density of population. On the other hand regions of subsistence agriculture (river valleys, deltas) support high population owing to high yields.
Industrially developed regions like Northwest Europe, Japan, Northeast USA, are densely populated as large number of people are engaged in industries, transport and communication, etc.
(c) Human Factors
politically disturbed areas have lesser population as people migrate to peaceful areas.
(d) Religious and Historical Factors
Religious and Historical Factors also create variations in the distribution of population. Industrial development in a particular area attracts by offering people better job opportunities and living conditions. This results in high density of population as in the case of North West Europe and Northeast America.