noun \ˌər-bə-nə-ˈzā-shən\ :
the process by which towns and cities are formed and become larger as more and more people begin living and working in central areas.
Urbanization refers to the increasing number of people that live in urban areas. It predominantly results in the physical growth of urban areas, be it horizontal or vertical.
According to the United Nations, urban population will increase more than 2.5 billion between 2010 and 2050 in less developed regions, compared to less than 150 million in its more developed regions. By 2050, more than 85 percent of the world’s urbanization is expected to be in today’s less developed regions.
As was noted in What is a Half Urban World? -
a considerable share of the world’s urban population lives in smaller urban areas (as small as 200 population). In 2013 is estimated that 51% of the world’s urban population lives in urban areas with less than 500,000 population, based on the data in Demographia World Urban Areas. The 10 largest urban areas, each with over 20 million population, account for approximately 6% of the urban population while the 28 megacities, each with more than 10 million population, account for 13% of the population. Approximately 21% of the urban population is in the more than 375 urban areas with between 1 million and 5 million population (Figure 1).