People are unevenly distributed around the world. The difference in distribution is measured by comparing population density - the number of people per square kilometre (km²).

Population density is determined more by environmental factors which make an area more or less attractive to settlers than by economic development.

Population patterns

The way in which people are spread across a given area is known as population distribution. Geographers study population distribution patterns at different scales: local, regional, national, and global.

Patterns of population distribution tend to be uneven. For example, in the UK there are more people living in the southeast of England than in Wales. 

Factors affecting population density

Environmental and human factors affect the spread of people across the world.

Factors attracting settlement

1. Temperate climate, eg the UK.
2. Low-lying flat fertile land, eg the Bangladesh Delta.
3. Good supplies of natural resources, eg building resources.

Factors discouraging settlement

1. Extreme climates, eg Sahara Desert.
2. Mountainous or highland areas, eg the Scottish Highlands.
3. Dense vegetation, eg the Amazon Rainforest.

Socio-economic factors

Factors such as the availability of jobs and comparatively high wages can contribute to high population density through migration. For example, from 2004 the UK has seen an influx of migrants from countries that have recently joined the EU, such as Poland.

Political factors

Civil war, eg in the Darfur region of Sudan, can contribute to lower population densities as people become refugees and leave an area.

• Areas of high and low population density are unevenly spread across the world.
• The majority of places with high population densities are found in thenorthern hemisphere.

Population numbers change over time, influenced by births, deaths and migration into or out of the area. Global population levels, having grown slowly for most of human history, are now rising.

Population pyramids show the structure of a population by comparing relative numbers of people in different age groups. Population structures differ markedly between LEDCs and MEDCs.

Demographic transition models show population change over time - and also show marked differences between LEDCs and MEDCs.

Global population growth

At present the world's population is growing quickly, though this has not always been the case.

• Until the 1800s the world's population grew slowly for thousands of years.
• In 1820 the world's population reached one billion.
• In the early 1970s, the world's population reached three billion.
• In 1999, less than 30 years later, the population doubled to six billion.
• The global rate of population growth is now one billion every 15 years.

Causes and rates of change

The three main causes of population change are:

• Births - usually measured using the birth rate (number of live births per 1000 of the population).
• Deaths - usually measured using the death rate (number of deaths per 1000 of the population) .
• Migration - the movement of people in and out of an area.

Rate of change

Births and deaths are natural causes of population change. The difference between the birth rate and the death rate of a country or place is called thenatural increase. The natural increase is calculated by subtracting the death rate from the birth rate.

natural increase = birth rate - death rate

The rate of natural increase is given as a percentage, calculated by dividing the natural increase by 10.