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:

Source: World’s Largest Cities Projection

Source: World’s Largest Cities Projection

Source: World’s Largest Cities Projection

Source: World’s Largest Cities Projection

Source: World’s Largest Cities Projection

Source: The Growth & Evolution of the World’s Largest Cities