World Population: Distribution and Growth

People are the most important resource of all, for it is people who use and value every other resource. But the world's population is spread very unevenly, and it is growing fast. Understanding where people live and why they cluster in some places is the starting point of human geography. So is understanding how population changes over time.

Population distribution means the way people are spread across the Earth. It is strikingly uneven: about half the world lives on only a small fraction of the land, while huge areas (deserts, high mountains, dense forests, frozen poles) have very few people.

A useful measure is population density, the number of people per square kilometre. Crowded countries like Bangladesh and parts of India and China have very high densities, while countries like Australia and Canada have very low ones. Fertile river valleys and industrial areas tend to be the most populated places of all.

The unevenness also follows latitude. About half of the world's population lives in the belt between 20°N and 40°N. This belt holds the great population clusters of East Asia, South Asia, and North Africa with the Middle East. The reason is simple. Most of the world's habitable land, fertile plains and great river valleys lie within it. As a result, the great majority of humanity lives in the Northern Hemisphere, which has far more land than the Southern Hemisphere.

Why do people cluster where they do? Several groups of factors decide it:

• Geographical factors: people prefer areas with a mild climate, plenty of fresh water, fertile soil and useful minerals or energy. They avoid extreme deserts, mountains and cold lands.
• Economic factors: jobs and opportunity draw people to industrial areas, cities and trade routes.
• Social and cultural factors: places of religious or cultural importance, and areas with good services, attract settlement.
• Political factors: stable, peaceful governments and supportive policies encourage people to stay.

Population change is the difference in the number of people over time. It happens through three processes:

• Births (natality): add to the population.
• Deaths (mortality): reduce it.
• Migration: the movement of people in (immigration) and out (emigration).

The natural growth rate is the birth rate minus the death rate. World population grew slowly for most of history. Then, after about 1800, it exploded. Medicine improved, food supply grew, and death rates fell. Birth rates stayed high, so the population surged. Such rapid growth strains resources, jobs and the environment.

As a country develops, its pattern of population growth changes. This is described by the demographic transition model, which has four stages:

• Stage 1: high birth rate and high death rate. Population grows slowly (pre-industrial society).
• Stage 2: death rate falls sharply (better food and medicine) while birth rate stays high. Population grows very fast.
• Stage 3: birth rate also falls (education, family planning, urban life). Growth slows.
• Stage 4: both rates are low. Population becomes stable.

Most developed countries have reached the later stages. Many developing countries are still passing through the rapid-growth stage. The model explains both the population explosion and its eventual slowing.