Urbanization (or urbanisation) is the physical growth of urban areas as a result of rural migration and even suburban concentration into cities, particularly the very large ones. The United Nations projected that half of the world's population would live in urban areas at the end of 2008. By 2050 it is predicted that 64.1% and 85.9% of the developing and developed world respectively will be urbanized.
Urbanization is closely linked to modernization, industrialization, and the sociological process of rationalization. Urbanization can describe a specific condition at a set time, i.e. the proportion of total population or area in cities or towns, or the term can describe the increase of this proportion over time. So the term urbanization can represent the level of urban relative to overall population, or it can represent the rate at which the urban proportion is increasing.
Urbanization is not merely a modern phenomenon, but a rapid and historic transformation of human social roots on a global scale, whereby predominantly rural culture is being rapidly replaced by predominantly urban culture. The last major change in settlement patterns was the accumulation of hunter-gatherers into villages many thousand years ago. Village culture is characterized by common bloodlines, intimate relationships, and communal behavior whereas urban culture is characterized by distant bloodlines, unfamiliar relations, and competitive behavior. This unprecedented movement of people is forecast to continue and intensify in the next few decades, mushrooming cities to sizes incomprehensible only a century ago. Indeed, today, in Asia the urban agglomerations of Dhaka, Karachi, Mumbai, Delhi, Manila, Seoul and Beijing are each already home to over 20 million people, while the Pearl River Delta, Shanghai-Suzhou and Tokyo are forecast to approach or exceed 40 million people each within the coming decade. Outside Asia, Mexico City, Sao Paulo, New York City, Lagos and Cairo are fast approaching or home to over 20 million people already.
A city is a relatively large and permanent settlement. Although there is no agreement on how a city is distinguished from a town within general English language meanings, many cities have a particular administrative, legal, or historical status based on local law.
For example, in the American state of Massachusetts an article of incorporation approved by the local state legislature distinguishes a city government from a town. In the United Kingdom and parts of the Commonwealth of Nations, a city is usually a settlement with a royal charter. Historically, in Europe, a city was understood by some to mean an urban settlement with a cathedral. The belief in this distinction is also common in England, where the presence of a cathedral is thought by many to distinguish a 'city' (sometimes called a 'cathedral city') from a 'town' (which has a parish church); the belief is incorrect (Chelmsford, for example, became a city only in 2012, but had a cathedral for most of the 20th century).