3. The Demographic Definition of a City This definition was first codified by sociologist Louis Wirth in his influential 1938 paper, “Urbanism as a way of life” (Wirth 1938). Cities, according to Wirth, are defined by four characteristics: 1. Permanence Has to be established and maintained for a while 2. Large population size Population has to exceed norms (e.g. U.S. = 10,000) 3. High population density People need to live in close proximity 4. Social heterogeneity Variety of people should live in the city Source: http://wideurbanworld.blogspot.com/2011/02/what-is-city-definitions-of-urban.html

6. Source: http://www.bbc.co.uk/news/world-asia-pacific-13800944 World’s Largest Cities - 2025 Projection

7. Source: http://www.bbc.co.uk/news/world-asia-pacific-13800944 World’s Largest Cities - 2025 Projection

8. Source: http://www.bbc.co.uk/news/world-asia-pacific-13800944 World’s Largest Cities - 2025 Projection

9. Source: http://www.bbc.co.uk/news/world-asia-pacific-13800944 World’s Largest Cities - 2025 Projection

10. Source: http://www.bbc.co.uk/news/world-asia-pacific-13800944 World’s Largest Cities - 2025 Projection

11. Source: http://www.riazhaq.com/2009/09/urbanization-in-pakistan-highest-in.html The Growth & Evolution of the World’s Largest Cities