In 2012, according to UN-Habitat, about 863 million people in the developing world lived in slums. As per UN Habitat a slum is characterized by lack of durable housing, insufficient living area, and lack of access to clean water, inadequate sanitation and insecure tenure. Around the world, there are about 1 billion slum dwellers, and the number is expected to grow to 1.4 billion by the year 2020. Slums form and grow in many different parts of the world for many different reasons. Some causes of slum development include rapid rural-to-urban migration, economic stagnation and depression, high unemployment, poverty, informal economy, poor planning, politics, natural disasters and social conflicts. Rural people migrate to urban areas in search for better jobs, better schools for their children and for diverse income opportunities. Improving quality of life in the slum is one of the Millennium Development Goals of the United Nations. Strategies tried to reduce and transform slums in different countries, with varying degrees of success, include a combination of slum removal, slum relocation, slum upgrading, urban planning with city wide infrastructure development, and public housing projects.