From CNN, writer Catriona Davies looks into how to best to improve the lives of slum dwellers.
A third of the urban population in developing regions lives in slums, according to U.N. Habitat, the United Nations department that focuses on urban development.
How to handle these makeshift settlements -- which often are overcrowded, lack adequate water supply and sanitation and whose residents' land rights are usually insecure -- is a challenge facing cities around the world.
Scroll over the interactive above to get a snapshot of slum populations in 14 countries around the world.
It's a problem that isn't going away. U.N. Habitat forecasts that the number of slum dwellers in the world will grow by 6 million a year and reach 889 million by 2020.
"First of all, city authorities need to acknowledge they have a slum problem and set targets for how to reduce it," said Eduardo Moreno, head of U.N. Habitat's Global Urban Observatory.
"Many cities automatically respond that they don't have slums or that they are very small, but data from U.N. Habitat shows it's more than the city authorities like to believe."
Moreno says governments need to invest heavily in reducing urban poverty and involve communities in their programs to improve slum conditions.
China, for instance, has reduced the proportion of its urban population living in slums by a quarter since 2000 by offering tax breaks to developers who build affordable homes, according to U.N. Habitat.
"The government has gradually been demolishing these areas and building new homes for people to move into," said Yiyi Lu, an expert in Chinese politics and social development at London-based think tank Chatham House and a research fellow at the University of Nottingham.
There are still large numbers of migrants living in relatively cheap accommodation on the outskirts of cities, she said, "but it is proper accommodation with basic facilities and is not concentrated in large scale areas."