The World’s Population: Distribution, Density and Growth

Why Population Spreads Unevenly

Distribution vs Density

• Distribution shows where people live across space, without asking how crowded that space is. It answers where, not how crowded.
• Density divides population by area, usually written as people per square kilometre. It answers how crowded, and lets very differently sized regions be compared fairly.
• Physiological density divides population by a country’s arable, cultivable land instead of its total area. It shows the real pressure a population puts on its farmland.
• A country can look huge in population yet show low density, simply because its area is huge too. Reading only one of the two figures can mislead.

What Pulls and Pushes Settlement

• Fertile river plains draw dense settlement: the Ganga, China’s Hwang-He and Chang Jiang, and Egypt’s Nile all show this pattern clearly.
• Jobs and industry pull people in too. Mineral belts like South Africa’s diamond mines and the Middle East’s oilfields, industrial hubs like Osaka and Mumbai, and culturally significant cities like Varanasi and Jerusalem all show dense clustering.
• Rugged terrain and harsh climate push settlement away instead. The Andes, Alps and Himalayas stay sparsely peopled for much the same reason deserts do, a dry Group B climate covered in our Koeppen climate classification article.
• Migration adds a third ingredient besides births and deaths. An emigrant leaves a country, and an immigrant arrives in one. The USA and Australia have gained population through immigration, while Sudan has lost population to emigration.

Measuring and Explaining Growth

The Demographic Transition Model

• Stage 1, High Stationary, has both high birth rates and high death rates, so population barely grows. This describes pre-industrial societies, where poor healthcare keeps death rates high alongside high birth rates.
• Stage 2, Early Expanding, sees death rates fall sharply once healthcare, sanitation and food supply improve, while birth rates stay high for a while longer. That gap drives rapid growth.
• Stage 3, Late Expanding, finally sees birth rates fall too, as urbanisation, education and family planning spread. Growth continues, but at a slowing pace.
• Stage 4, Low Stationary, settles both rates at low levels, so growth flattens out again, just like Stage 1. But the reason is opposite: low death and low birth this time, not high and high.

Growth Rates, Doubling Time and Milestones

• Crude birth and death rates count births or deaths per 1,000 people in a year. Subtracting the death rate from the birth rate gives the natural growth rate, the growth from births and deaths alone, ignoring migration.
• Doubling time is how long a population takes to double at its current growth rate. A faster growth rate mechanically produces a much shorter doubling time, which is why even a small rate difference matters hugely over decades, as this site’s own India population growth phases article shows for a single country.
• World population reached 1 billion in 1804. It took just 155 more years to reach 3 billion, in 1959, and only 40 more years to double again, to 6 billion, in 1999.

Where the World’s Growth Is Happening Now

• Most developed countries have already reached Stage 4, with slow or even shrinking populations, a pattern reflected in the ageing pyramid shapes covered in our Population Composition article.
• Developed countries industrialised earlier, so their death rates and then their birth rates fell decades ago. Many developing countries only saw death rates fall recently, while birth rates are still catching down.
• The term population explosion describes Stage 2’s very rapid growth: death rates have crashed by then, but birth rates have not yet followed. It is a temporary phase in the model, not a permanent state.