The world's urban population in 1950 of just 746 million has increased to 3.9 billion in the decades since. In 2009, the number of people living in urban areas (3.42 billion) surpassed the number living in rural areas (3.41 billion) and since then the world has become more urban than rural. This was the first time that the majority of the world's population lived in a city. In 2014 there were 7.2 billion people living on the planet, of which the global urban population comprised 3.9 billion. The Population Division of the United Nations Department of Economic and Social Affairs at that time predicted the urban population would grow to 6.4 billion by 2050, with 37% of that growth to come from three countries: China, India and Nigeria.
Unlike an urban area, a metropolitan area includes not only the urban area, but also satellite cities plus intervening rural land that is socio-economically connected to the urban core city, typically by employment ties through commuting, with the urban core city being the primary labor market.
European countries define urbanized areas on the basis of urban-type land use, not allowing any gaps of typically more than 200 metres (220 yd), and use satellite imagery instead of census blocks to determine the boundaries of the urban area. In less-developed countries, in addition to land use and density requirements, a requirement that a large majority of the population, typically 75%, is not engaged in agriculture and/or fishing is sometimes used.
Argentina is highly urbanized. The ten largest metropolitan areas account for half of the population, and fewer than one in ten live in rural areas. About 3 million people live in Buenos Aires City and the Greater Buenos Aires metropolitan area totals around 15 million, making it one of the largest urban areas in the world, with a population of 18 million all up.