An urban area is the region surrounding a city. Most inhabitants of urban areas have non-agricultural jobs. Urban areas are very developed, meaning there is a density of human structures, such as houses, commercial buildings, roads, bridges, and railways.

"Urban area" can refer to towns, cities, and suburbs. An urban area includes the city itself, as well as the surrounding areas. Many urban areas are called metropolitan areas, or "greater," as in Greater New York or Greater London.

When two or more metropolitan areas grow until they combine, the result may be known as a megalopolis. In the United States, the urban areas of Boston, Massachusetts, eventually spread as far south as Washington, D.C., creating the megalopolis of BosWash, or the Northeast Corridor.

Rural areas are the opposite of urban areas. Rural areas, often called "the country," have low population density and large amounts of undeveloped land. Usually, the difference between a rural area and an urban area is clear. But in developed countries with large populations, such as Japan, the difference is becoming less clear. In the United States, settlements with 2,500 inhabitants or more are defined as urban. In Japan, which is far more densely populated than the U.S., only settlements with 30,000 people or more are considered urban.

Throughout the world, the dominant pattern of migration within countries has been from rural to urban areas. This is partly because improved technology has decreased the need for agricultural workers and partly because cities are seen as offering greater economic opportunities. Most of the world's people, however, still live in rural areas.

Towns

One type of urban area is a town. A town is generally larger than a village, but smaller than a city. Some geographers further define a town as having 2,500 to 20,000 residents.

Towns usually have local self-government, and they may grow around specialized economic activities, such as mining or railroading.

The western part of the United States, for instance, is dotted with "ghost towns." Ghost towns no longer have any human population. They are full of abandoned buildings and roads that have been overtaken by shrubs and natural vegetation.

Many ghost towns in the western U.S. are the remains of "boom towns," which developed after gold or silver were discovered in the area in the 19th century. Economic activity boomed in these towns, most of it centered on mining. When all the gold and silver was mined, economic activity stopped and people moved away, leaving ghost towns of empty homes and businesses.

Growth of Suburbs

Suburbs are smaller urban areas that surround cities. Most suburbs are less densely populated than cities. They serve as the residential area for much of the city's workforce. The suburbs are made up of mostly single-family homes, stores, and services.

Many city residents move to suburbs, a situation known as suburban migration. Homes in suburbs are usually larger than homes in cities, and suburbs usually have more parks and open spaces. Residents may move to escape the traffic, noise, or to enjoy a larger residence.

Large groups of Americans began to move to suburbs in the late 1800s. The invention of the streetcar made it possible for residents to commute from their homes to their city jobs.

At the end of World War II, the U.S. government enacted a program that gave home loans to returning war veterans. This created an explosion of single-family homes and increased the growth of suburbs across America.

The establishment of the Federal-Aid Highway Act of 1956 also contributed to the growth of suburbs and urban areas. The Highway Act created 66,000 kilometers (41,000 miles) of interstate roadway systems. The original plan for the highway system was for the evacuation of large cities in case of a nuclear or military attack. What the Highway Act created instead was suburban sprawl.

Suburban sprawl continues to be a phenomenon in the U.S. First, outlying areas of a city widen. Slowly, these outlying areas become more crowded, pushing the suburbs farther into rural areas.

Housing and businesses that serve suburban communities eat up farmland and wilderness. More than 809,000 hectares (two million acres) of farmland and wilderness are lost to development every year in the U.S.

Smart Growth

Recently, experts have tried to curb the spread of suburban sprawl, or at least create urban areas that are developed more purposefully. This is known as "smart growth." City planners create communities that are designed for more walking and less dependency on cars. Some developers recover old communities in downtown urban areas, rather than develop the next piece of farmland or wilderness.

U.S. states such as Oregon are passing laws to prevent unplanned urban sprawl. They have created boundaries around cities that limit the growth of development. Officials have created laws stating that the minimum size of a plot of land is 32 hectares (80 acres). This is to prevent developers from creating suburban communities. An 80-acre plot of land is too costly for a single-family home!

Other smart-growth communities are creating new types of development. Some have large amounts of undeveloped "green space," organic farms, and lakes.

Urban areas typically drain the water from rain and snow, which cannot collect in the paved-over ground. Rather than use drainage pipes and ditches, smart-growth communities create wetlands designed to filter storm runoff.

More city planners are developing urban areas by considering their geography. Engineers build structures that blend with their natural surroundings and use natural resources. White roofs, for example, reflect the sun's rays and lower the cost of air conditioning. Homebuilders in urban areas as diverse as Los Angeles, California, U.S., and the island communities of Greece create homes and businesses with white plaster or tile roofs for this reason.

There is also a move toward preserving and maintaining more green areas and planting more trees in urban areas. Landscape designers often consult with city planners to incorporate parks with development.