Population and urbanisation

Urbanisation

HintThe countryside empties as the built-up areas swell.

The whyIt is measured as the percentage of people living in urban areas, and worldwide that share passed half around 2007. Cities grow both by people arriving and by the residents already there having children.

Flat lowland

HintEasier to farm, easier to build on, easier to cross.

The whyGentle relief, deep soil, a mild climate and fresh water draw people in; deserts, high mountains, dense rainforest and frozen tundra push them away. Half the world lives on a small fraction of the land surface.

A fording point

HintEvery road funnels towards the one shallow place travellers could wade over.

The whyOxford grew at exactly such a crossing, because all the traffic converged there. Other classic site factors are a wet point spring line, a dry point above the flood, and a defensive hilltop or meander loop.

Natural change

HintIt ignores anyone moving in or out; only births and deaths count.

The whyIf births outnumber deaths the figure is positive and the population grows with nobody arriving at all. Migration is counted separately, and the two added together give the total.

Stage 2

HintClean water and medicine arrive well before family sizes shrink.

The whyBetter sanitation, food and medicine cut deaths sharply while families are still large, so the population booms. Births only fall at the next step, as children survive, women work and education spreads.

push

HintA reason to leave, not a reason to arrive.

The whyWar, drought, unemployment and persecution drive people away. Jobs, safety, schools and relatives already settled draw them somewhere else. Most journeys are a mixture of both halves.

Rural-urban migration

HintThe one-way journey from field to factory.

The whyIt is the single biggest driver of city growth in lower-income countries. Poor harvests and low wages push people out, while jobs, schools and hospitals pull them in.

Ten million

HintRoughly the population of Portugal or Greece, packed into one place.

The whyThe United Nations sets the bar there. Tokyo, Delhi and Shanghai lead the list, and almost every new one is appearing in Asia or Africa rather than Europe.

An informal settlement

HintWith no legal deeds, the city will not lay on pipes or power.

The whyDharavi in Mumbai and Rocinha in Rio grew where the city gained people faster than it built homes. What residents lack is secure land title, clean water and sanitation - not skill or effort.

The Human Development Index

HintThe UN publishes it each year, scored from zero to one.

The whyIncome on its own can hide huge inequality, so this score adds life expectancy and years of schooling. A figure near 1 means long, educated, prosperous lives; near 0 the opposite.

The development gap

HintThe distance between the two ends of the world's wealth ladder.

The whyIt is not random: colonial history, debt, climate, being landlocked and the low prices paid for raw exports all feed it. The same divide exists inside countries, between a capital city and its rural regions.

Emergency aid

HintBlankets, clean water and medics within days, not a school built over years.

The whyIt saves lives but changes nothing once it stops. Long-term projects build wells, clinics and training, while fairer trade prices and debt relief move far more money than donations ever do.