1. the trend toward living in cities, which are defined by the United States Bureau of the Census as having populations of 50,000 or more.

2. the process of becoming a community with urban characteristics. In the early 20th century, psychological research on urbanization initially focused on the impact of urban life on mental health, purporting to find a link between inner-city residence and increased rates of mental illness; this position was later qualified (see drift hypothesis). Inquiry has since expanded to investigate the psychological, physical, and behavioral consequences of the urban environment (e.g., population density, crowding, noise, and pollution) and the social, economic, and cultural dimensions of city life. See also urban ecology. —urbanize vb.