A slum is an area of very poor housing where people live in overcrowded conditions and without the basic needs of everyday life.

Slums occur because people are not paid enough to live in better housing, and or because the number of people moving in to a city is greater than the number of houses of good quality that can be built and paid for.

Slums were common as towns and cities grew. There were slums all around European cities through the Middle Ages. As people moved, or were forced, from farms in Tudor times many people moved to cities, and there they found rooms in poor housing that people had put up in their back gardens. The video shows you what that was like.

Most European and American cities had large areas of slums right up to the early 20th centuries, and they were lived in by people working in factories for very low wages, so they could not afford any better.

But over time, wages improved and governments replaced slums with social housing, where fair rents were charged. Slums are now rare in cities in prosperous countries.

But in the developing world the conditions that were found in Europe and America are now found in Africa, South America and Asia because there people are moving to cities just as was the case in Europe and America centuries ago. The number of these people is rising fast, just as it did in 19th century Europe and America, and so most people have very low wages. As a result, they have to find what housing they can. Many people make their own houses out of old cartons, plastic sheet and wood.

For geographers studying slums, there are two kinds. Slums are really just very poor and crowded housing made of bricks. But the self-build houses of wood and plastic sheet are an even poorer version of slums. We call them shanty towns. They are often built illegally on land they do not own, and their shanties are often bulldozed away, so they have to start all over again.

These terrible conditions will only change when people and the countries start to earn more money so that better housing can be built, and they can afford to pay for it. We are a long way from that at the moment.