Urban and suburban areas differ greatly in the simplest of ways: Urban areas are built up while suburban areas are spread out. Urban areas have a far greater concentration of people within their boundaries while suburban areas have far more space per person. According to the US Census bureau, a certain population within the defined boundaries of an incorporated or unincorporated area constitutes an urban area. But population count or density is not the only way to differentiate between suburban and urban entities.
Urban areas are centers of culture, government, higher education, often for entire regions. Urban areas are major hubs for public transportation of people, and have much more public transportation options within their general boundaries. Urban areas are also hubs for the transport of people and goods from other regions and countries, along waterways, train, highway, and air corridors.
The term "metropolis" is applied to urban areas when the population of a defined and incorporated area exceeds one million. In some cases, a built up city can have a concentrated population at it's core while it is surrounded by more spread out areas that have more space between structures, or both urban and suburban components.
Suburbs tend to grow up around urban areas as the topography allows. It is common for the residents of suburbs to travel into the urban areas in order to work, shop, study, recreate, or do business at the centralized shopping, financial, government, medical, educational and other locations in the urban core.
Suburbs attract the manufacturing or industrial operations, while the abandoned urban manufacturing facilities are converted to housing, light industrial, or commercial uses within the urban core. The working class finds it more financially viable and personally satisfying to live in the suburbs, while the professional and upper classes can afford to live and work in the urban cores.
As a result, urban areas can also be distinguished from suburban areas in strongly contrasting elements of blight and rejuvenation. In the urban cores, there are stark differences in income which range from the highest possible incomes, to below poverty level. Homeless individuals can function in urban areas because of the available public transportation and the more well established formal and informal support systems that are developed for the extremely poor and homeless. The exceedingly wealthy enjoy the urban areas because of the cultural, financial and social attractions as well as the luxury services available. The middle class and working class can tend to find the cities to be financially accessible only for visiting to work, shop, and to enjoy cultural and other regional attractions and centralized functions.
Suburban areas have a characteristic lack of easily accessed public transportation and are heavily populated and transited by private vehicles. In some suburban areas, the housing, commercial, government and work centers are so widely spaced apart that it is necessary to have a private vehicle in order to function in life. As a result, massive segments of suburban space are allotted for parking, moving from one point to another, sales, refueling and maintenance of vehicles. The car is far more a part of life in suburbia. The suburban homeless find it far more difficult to get from one place to another for services or for survival.
While cities are generally static entities, suburbs can be very dynamic entities. Cities can grow from what were once suburbs as populations grow and more decentralized centers of government, services, culture and other features of cities are built.
Finally, there is no single number of people, number of people per square mile, or even definition of suburban area that is agreed upon throughout the world. Suburbs can form around, near, or even far away from cities, but are definitely more residential in nature than cities. Suburban businesses tend to be far more oriented to the service sector of the economy.