Thursday, January 19, 2012


Population distribution and density 
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.

Population density
Population density is the average number of people per square kilometre. It is a way of measuring population distribution and shows whether an area is sparsely or densely populated. Population density is calculated using the following formula:

Population density = total population ÷ total land area in km²

Population density
The map shows patterns of population density on a global scale. Note that:
  • areas of high and low population density are unevenly spread across the world
  • the majority of places with high population densities are found in the northern hemisphere
Map of the world showing population density 

The population density of a country is has very little to do with its level of economic development. For example, both Bangladesh and Japan are very densely populated, but Bangladesh is a LEDC (Less Economical Developed Countries) and Japan is a MEDC (More Economical Developed Countries). 

Factors affecting population density
Environmental and human factors affect the spread of people across the world.

Factors attracting settlement
temperate climate, eg the UK
low-lying flat fertile land, eg the Bangladesh Delta
good supplies of natural resources, eg building resources

Factors discouraging settlement
extreme climates, eg Sahara Desert
mountainous or highland areas, eg the Scottish Highlands
dense vegetation, eg the Amazon Rainforest
Socioeconomic 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.

Global population growth
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.
  • 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.
The graph shows this pattern of accelerating growth (including the predicted population for 2025).

World population growth 500BC - 2025

Causes and rates of change
The three main causes of population change
  • Births - usually measured using the birth rate (number of live births per 1,000 of the population per year).
  • Deaths - usually measured using the death rate (number of deaths per 1,000 of the population per year).
  • 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 the natural 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. For example, if the birth rate is 14 per 1,000 population, and the death rate is 8 per 1000 population, then the natural increase = 14 - 8 = 6. That is 6/1000, which is equal to 0.6 per cent.

Patterns of population growth
Rates of population growth vary across the world. Although the world's total population is rising rapidly, not all countries are experiencing this growth. In the UK, for example, population growth is slowing, while in Germany the population has started to decline. MEDCs have low population growth rates, with low death rates and low birth rates.

  • Population will decline if death rate is greater than birth rate.

  • Population will increase if death rate is less than birth rate.

LEDCs have high population growth rates. Both birth rates and death rates in LEDCs tend to be high. However, improving healthcare leads to death rates falling - while birth rates remain high.

The table shows data in selected LEDC and MEDC countries. The figures are per 1,000 of the population per year.

CountryBirth rateDeath rateNatural increasePopulation growth rate (%)
CountryBirth rateDeath rateNatural increasePopulation growth rate (%)
South Africa2515101
In Bulgaria, the birth rate is 9/1,000 and death rate is 14/1,000. As birth rate is less than the death rate, Bulgaria has a declining population. In South Africa, the birth rate is 25/1,000 and death rate is 15/1,000. South Africa has an increasing population with a population growth rate of 1 per cent.

The demographic transition model
The demographic transition model shows population change over time. It studies how birth rate and death rate affect the total population of a country. The five stages of the demographic transition model
  1. Total population is low but it is balanced due to high birth rates and high death rates.
  2. Total population rises as death rates fall due to improvements in health care and sanitation. Birth rates remain high.
  3. Total population is still rising rapidly. The gap between birth and death rates narrows due to the availability of contraception and fewer children being needed to work - due to the mechanisation of farming. The natural increase is high.
  4. Total population is high, but it is balanced by a low birth rate and a low death rate. Birth control is widely available and there is a desire for smaller families.
  5. Total population is high but going into decline due to an ageing population. There is a continued desire for smaller families, with people opting to have children later in life.
As a country passes through the demographic transition model, the total population rises. Most LEDCs are at stage 2 or 3 (with a growing population and a high natural increase). Most MEDCs are now at stage 4 of the model and some such as Germany have entered stage 5.

The demographic transition model

As populations move through the stages of the model, the gap between birth rate and death rate first widens, then narrows. In stage 1 the two rates are balanced. In stage 2 they diverge, as the death rate falls relative to the birth rate. In stage 3 they converge again, as the birth rate falls relative to the death rate. Finally in stage 4 the death and birth rates are balanced again but at a much lower level.

Limitations of the model
  1. The model was developed after studying the experiences of countries in Western Europe and North America. Conditions might be different for LEDCs in different parts of the world.
  2. The original model doesn't take into account the fact that some countries now have a declining population and a 5th stage. Most texts will now show this stage as it is relevant to an increasing number of MEDCs in the 21st century.
Population structure and population pyramids
Population structure means the 'make up' or composition of a population. Looking at the population structure of a place shows how the population is divided up between males and females of different age groups. Population structure is usually shown using a population pyramid. A population pyramid can be drawn up for any area, from a whole continent or country to an individual town, city or village.

The following graphs show the population pyramids of an MEDC (the UK) and an LEDC (Mozambique), for 2000 and in 2025 using projected figures. The left side of each pyramid shows the number of men in each age group, the right side shows the number of women in each age group.

Projected population pyramid for the UK 2025

Compare this to the 2025 pyramid, which would be stage 5 in the model. Here the bulge extends much further, covering the age groups 30-64, with the numbers beginning to reduce significantly only after 64.

Now compare the UK population pyramids with those for Mozambique:

Population pyramid for Mozambique 2000

In this graph, notice that in 2000 the 0-4 age group contained the largest number of people, with the numbers thereafter declining steadily as the ages increase. The graph matches stage 1 in the model.

Projected population pyramid for Mozambique 2025

In the second graph, the largest group in Mozambique in 2025 is still the 0-4 age group, but there are nearly as many people in the 5-29 age groups. Now the population pyramid matches stage 2.

Analysing population pyramids
Key things to know about population pyramids
  • The shape of a population pyramid can tell us a lot about an area's population.
  • It gives us information about birth and death rates as well as life expectancy.
  • A population pyramid tells us how many dependants there are. There are two groups of dependants; young dependants (aged below 15) and elderly dependants (aged over 65).
  • Dependants rely upon the economically active for economic support.
  • Many LEDCs have a high number of young dependants, whilst many MEDCs have a growing number of elderly dependants.
How do pyramids change over time?
  • A population pyramid that is very triangular (eg Mozambique in 2000) shows a population with a high number of young dependants and a low life expectancy.
  • A population pyramid that has fairly straight sides (more like a barrel) shows a population with a falling birth rate and a rising life expectancy.
  • Over time, as a country develops, the shape changes from triangular to barrel-like.
  • Places with an ageing population and a very low birth rate would have a structure that looks like an upside-down pyramid.

Courtesy: BBC

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