For the first time in human history the urban population outnumbers the rural one. This is both due to villages growing to become towns and cities, and migration of the rural population to urban cities. According to the UN’s calculations, in 2003 870 million people lived in slums, and this figure was estimated to increase to 1.43 billion by 2020. And while up until the 1950s it was thought that these settlements were transitory, providing cheap housing to the poor until they improved their economic circumstances, it soon became apparent that for most slum dwellers these settlements were more permanent residences.