Louis Wirth argues that urbanism is defined by human population growth and sociological aspects. He defines a city as a large, dense, and permanent settlement of socially diverse individuals. Wirth uses population size, density, and social heterogeneity to show how cities have grown and their inhabitants have become more individualistic and less familiar with one another. However, the author believes other factors beyond a city's qualities, such as immigration policies, can also affect citizens' personalities and levels of social heterogeneity. While Wirth explores urbanism in detail, his definition is not fully specified.