Human geography: where people live

There are about 8 billion people on Earth, but they are spread out very unevenly. Some regions are packed shoulder-to-shoulder with millions of inhabitants per square kilometer; other regions are almost empty. Why? Geography (mountains, climate, fresh water, soil) sets the stage, but human choices (jobs, war, opportunity, family) decide where people actually end up living.

Population density

Population density is the number of people living in a given area, usually counted as people per square kilometer (or per square mile). Bangladesh has more than 1,200 people per km² — extremely high. Canada has about 4 people per km² — very low, because most of Canada's land is cold taiga or tundra where farming is hard. Density tells you how crowded a place is, but it does not say anything about wealth: Monaco is very dense and very rich; Bangladesh is very dense and poorer.

Urbanization

For most of human history, the vast majority of people lived in the countryside and farmed for a living. In 1800, only about 7% of people on Earth lived in cities. In 2007 that number passed 50%, and today more than half the world's population lives in urban areas — the shift is called urbanization. Big cities offer jobs in factories, offices, and services that simply do not exist in rural villages. The drift from country to city is one of the defining stories of the modern world.

Push factors and pull factors

Geographers explain migration with two ideas. A PUSH factor is something that drives people AWAY from where they live — war, poverty, persecution, drought, natural disaster, lack of jobs. A PULL factor is something that attracts people TO a new place — jobs, safety, better schools, family connections, freedom of religion. Most migration is a combination: people are pushed by one set of forces and pulled by another.

• Push factors: war and violence, poverty, persecution, famine, drought, natural disasters, climate change, lack of jobs.
• Pull factors: better-paying jobs, safety, freedom of religion or speech, family already there, better schools or healthcare, more opportunity.

Megacities

A megacity is a metropolitan area with more than 10 million people. In 1950 there were only two megacities (New York and Tokyo). Today there are more than 30. The biggest is Tokyo, Japan, with about 37 million people. Delhi (India), Shanghai (China), São Paulo (Brazil), and Mexico City (Mexico) are all home to more than 20 million people each. Most of the fastest-growing megacities today are in Asia and Africa, where rural people continue to flow into the cities.

Where people DO live and where they DO NOT

About 90% of the world's population lives in the northern hemisphere, because most of the land sits there. Within continents, people cluster along coasts, river valleys, and temperate climate zones. Deserts (the Sahara, the Outback, the Arabian Peninsula interior), high mountains (most of the Himalayas, the Andes peaks), polar regions (Antarctica, much of Siberia), and the deep Amazon are sparsely populated. The map of where people live is, fundamentally, a map of where the climate is moderate, fresh water is plentiful, and soil is fertile.