Areas with low population densities tend to be steep, rugged mountains where soils are thin and air pressure is low (such as the Andes Mountains of South America) or high plateaux (such as Tibet).

Areas where manufacturing industry has been established for many decades, or even centuries, usually have high population densities. Some examples of densely populated manufacturing regions include north-east China (also known as Manchuria), and the north-east of the United States.

Areas where farming is difficult, perhaps because of climate, landforms or soils, have sparse populations, with some examples being the Sahara Desert

Areas where it is physically easy and financially viable to construct communications infrastructure, such as ports, canals, roads, railways and airports, attract people and therefore tend to have high population densities. Examples of such areas include the United Kingdom, Singapore and Hong Kong.

Government policies and decisions can cause areas to become either more densely population or less densely populated. Areas can become more densely settled when governments decide to develop new areas (such as mining settlements in the Russian Far East, or create new cities such as Shenzhen in China.

A reliable water supply is essential for human survival, and people are attracted to areas where the availability of water is sufficient without being excessive. Areas with high population include places with reliable, evenly distributed rainfall (such as western Europe and north-eastern United States).

People avoid areas where there are dangerous pests and diseases. Therefore, places such as the lowlands of Papua New Guinea and parts of central Africa have sparse population densities because of malaria.

People are attracted to areas with major concentrations of minerals or energy resources, such as the Pittsburgh region of the USA, South Wales in the UK, and the Ruhr basin of Germany.

Some places with abundant natural resources may have sparse population densities, either because the resources can be obtained with very few people (such as oil in Algeria, Iran or Saudi Arabia), or because the resources have not been developed (such as minerals in Eritrea or the Russian Far East).

Population densities can also become sparser over time due to depopulation arising from political conflict, and some examples of this include Syria, Afghanistan, Somalia, Sudan and South Sudan.

Areas that do not receive adequate investment are often sparsely populated or become depopulated, examples being parts of the Russian Far East and declining manufacturing areas in Eastern Europe.

Areas with soils that make cultivation difficult usually have sparse populations. Soils may be unsuitable for cultivation because they are frozen (the permafrost soils of Siberia), they are leached and therefore low in minerals and nutrients (rainforest soils in the Amazon Basin), they are thin and poorly developed (mountainous areas of the Himalayas in Asia).