Urban planning can be defined variously as the formulation of alternative patterns of urban settlement, the rational use of resources to alleviate urban problems, and the provision of a city's physical and social infrastructure--transportation, utilities, housing, community facilities, and services. More simply, it is the art of building cities. Today planning is as much a part of the responsibility of urban government as the provision of services or the collection of taxes. Municipal governments prepare comprehensive or master plans to guide future development, capital budgets to program future expenditures for services, and zoning ordinances and subdivision regulations to control development. Contemporary urban planning draws upon many disciplines. The social sciences quantify the size and characteristics of the future population, its needs, and its occupational structure and income distribution. \Tarchitecture\t, \Tengineering\t, \Tlandscape architecture\t, and urban design provide the three-dimensional solutions that are the expression of broad development policy decisions. The science of ecology permits an increasingly accurate measurement of the environmental consequences of development and the control of their adverse effects. Law and political science provide the principal legislative and bureaucratic mechanisms that are used to implement planning decisions. Planning, however, is far from an exact science. Its prime area of concern is people and their relationship to the built environment. Although planning may anticipate the need for jobs, shelter, transportation, education, health, or recreation, its effectiveness is limited to putting restraints on private property rights and providing incentives to influence individual choices. Planning is a repetitive or iterative process. It requires the formulation of social goals that can be translated into politically acceptable objectives that, in turn, can be detailed into specific programs and projects. Although social values and goals tend to evolve rather slowly, their transformation into operative programs tends to reflect immediate political objectives. The 2- to 4-year terms of city officials often dictate the periods over which the effectiveness of planning is measured and thus determine the scope of many local programs and projects. Planning is also a dynamic process. Population movements, economic fluctuations, technological innovations, or, more commonly, the obsolescence of the city's physical plant require periodic revisions of planning strategies. HISTORY OF URBAN PLANNING The human desire to shape the urban environment goes back to the earliest known cities that developed in the Fertile Crescent and in India between 5000 and 3500 BC. Even though ancient cities were small by modern standards, their populations were frequently crowded within a defensive wall. Developmental pressures within a restricted area almost certainly resulted in legal restrictions regarding private property rights. The city's rulers built and maintained works of public utility--defensive walls and citadels, bridges and roads, temples and markets--while laws protected public ways and private property from encroachments. Urban Planning in the Ancient World Ancient civilizations occasionally planned new cities or major additions to existing settlements. The most widespread plan was a rectangular or grid street pattern that allowed considerable flexibility in the size of blocks while maintaining a clear visual order. Noteworthy examples of this type of city plan include Kahun (Egypt, c.1890 BC), whose workers' quarter is separated by an internal wall from the wealthier districts; \TMiletus\t (Anatolia, 479 BC), whose reconstruction, following its destruction (494 BC) by the Persians, was carried out in strict accord with the planning principles attributed to the Greek planner \THippodamus of Miletus\t; and \TTimgad\t (Algeria, AD 100), one of a series of colonies for Roman veterans of Emperor Trajan's army that were built to protect the fertile coastal plain from nomadic raiders. Vitruvius By the 4th century BC a theory of urban planning already existed, as evidenced in the writings of Hippocrates, Plato, and Aristotle. It addressed issues of site selection and orientation, as influenced by natural features and climate; city form, including the optimal location for major buildings; the size and composition of the population; and urban government and laws. These theories were later modified and amplified into a veritable textbook on urban planning, \TVitruvius\t's De architectura (after 27 BC; trans. as Ten Books on Architecture, 1826 and 1914). This work standardized the city plans that the Roman engineers used in the innumerable fortified settlements and provincial cities that they built throughout the empire. The typical Roman plan, vestiges of which are still clearly discernible in many cities of Europe, North Africa, and the Near East, consisted of two perpendicular main streets running north-south (cardo) and east-west (decumanus) with the city's main civic and mercantile square (forum) located at their intersection. Other uses were allocated in various ways among the four quadrants, whose streets ran parallel to the cardo and decumanus. Very large buildings, such as the amphitheater, were often relegated to the city's periphery, as were slaughterhouses and other unpleasant necessities. Extensive public works were carried out in larger Roman cities, both of a utilitarian--aqueducts, sewers, harbor, markets--and of a social nature--public baths, gardens, library, amphitheater. In 3d-century Rome building regulations prescribed construction standards, maximum allowable building heights on public ways, and minimum setbacks from other buildings. At various times the imperial government interfered directly in housing, forcing owners to rebuild fire-damaged structures under penalty of confiscation (edict of Vespasian, AD c.70) and to repair dilapidated buildings (edict of Hadrian, AD c.129). Streets were widened to accommodate the growing number of heavy wagons, whose nighttime movement was banned (edict of Julius Caesar, 44 BC) as was the encroachment of stalls and shops on the public way (under Domitian, r. AD 81-96). Medieval European Cities Most of the Roman planning regulations fell into disuse during the protracted period of urban decadence that followed the dismembering (AD 476) of the empire, and they were not revived when European cities started flourishing again in the 10th and 11th centuries. They were replaced by a system of customary obligations that assigned to burgesses and guilds, or to work parties of residents, such traditional responsibilities of urban government as clearing refuse, maintaining highways, keeping the watch, and even repairing the city's walls. Even when a city's fortifications were extended to relieve overcrowding or to annex settlements beyond the walls, little effort was made to regulate the development of private property. Urban statutes, whether granted by charter or derived from local customs, were primarily concerned with collecting tolls and taxes, regulating the activities of the craft and merchant guilds, and ensuring an adequate supply in the town's markets. Revival of the Rectangular Grid Plan Occasionally, the establishment of a new settlement provided an opportunity to create a physical order in sharp contrast to the more or less tortuous pattern of most medieval cities. The simple geometry of the rectangular grid plan prevailed again, as in ancient times, in such late-medieval French bastides as Aigues-Mortes (1240) or Montpazier (1284)--new towns whose royal charters freed their inhabitants from feudal obligations and granted them advantageous trading privileges--and in the northern European trading cities of the Hanseatic League. Medieval theories of the city form were explicitly stated in Albrecht Durer's idealized fortified capital of a kingdom in Etliche Underricht zu Befestigung der Stett, Schlosz und Flecken (1527; Guide to the Fortification of City, Castle, and Town), whose rigid spatial organization grouped classes by social status and segregated such noxious buildings as slaughterhouses, tanneries, and ironworks. Renaissance Urban Planning The shape of the city became more complicated as a result of improvements in the techniques of war and the reawakened interest in urban aesthetics in the Renaissance. The greater power of siege artillery required the replacement of vertical city walls with angular fortifications, whose sloping planes deflected the impact of iron cannonballs. Aesthetically, cities were embellished by widening streets and opening up squares within the dense medieval fabric and by building new churches, town halls, and palaces. Straight avenues culminating in a monumental square ornamented with symmetrical buildings in the classical style became fashionable in the more prosperous European cities. Starting in the middle of the 15th century, Italian theorists created a voluminous body of literature on the theory of urban planning. Largely inspired by Vitruvius, it treated aesthetics as well as such pragmatic questions as the design of fortifications, construction techniques, the location of specific facilities, and the supply of water. The theories of Leon Battista \TAlberti\t in De re aedificatoria (c.1450; trans. as On Architecture, 1726) and of Andrea \TPalladio\t in I quattro libri d'architettura (1570; trans. as The Four Books of Architecture, 1716), among many others, established an urban style whose influence was felt throughout the Western World. The aesthetic principles of the time were given their full rein in the layout of new towns: Palmanova (Italy, 1593), Willemstad (The Netherlands, 1583), and Versailles (France, 1665) exemplify the symmetry, the use of broad avenues leading to main squares, and the clear street patterns advocated by the Italian theorists. The creation of an orderly urban environment naturally led to the formulation of development controls to preserve it. The plan prepared for a fourfold extension of Amsterdam (The Netherlands, 1612) offers an exceptional example of a comprehensive effort to combine aesthetic and functional aspirations. Its three wide concentric canals, interconnected by smaller waterways radiating from the old town center, delineated a series of functional zones, with strict development controls governing the frontage of buildings on the canals, the use to which they could be put, their maximum height, and the general appearance of the building facade. These regulations were enforced through covenants between the Town Council, which had reclaimed the land and constructed canals and streets, and the purchaser of each lot. Similarly, the Act for Rebuilding the City of London (1667), following the great fire of 1666, not only provided for the widening of streets and the opening of new avenues but also specified the height, general appearance, and materials to be used in the new buildings. The influence of Renaissance planning is also to be found in many of the new cities founded by Europeans in the Americas and in Asia. The Spanish colonial cities owed their rectangular plan and main square surrounded by the principal church and the government building to the Royal Ordinances of 1573 (Leyes de las Indias). William Penn's plan for Philadelphia (1682) and that for Montreal (1672) embodied the accepted planning principles of the time: straight streets and one or more public squares on which the principal buildings were located. ORIGINS OF CONTEMPORARY PLANNING Many of the problems that still plague our cities--slums, environmental pollution, social and economic segregation--came about during the Industrial Revolution. The incapacity of urban governments to enlarge their traditional responsibilities at a time when cities were developing rapidly led to the proliferation of substandard buildings, the intermingling of noisome industries and housing, and a density of development that overtaxed primitive water supplies and sewerage systems. Conditions in Manchester, England, in the 1830s were symptomatic of the urban deterioration that was taking place. The city's population had more than doubled in 30 years, and almost half of the housing units were slums. No less than 15% of the dwellings were damp cellars, and 20% had their only access to light and air through narrow passages, often less than 2 m (6 ft) wide; more than 80% of the dwellings had no running water, and 30 or more families commonly shared an outdoor privy; fewer than half of the streets were paved; refuse was collected only monthly in the poorer districts. At the end of the 19th century, almost 40% of the population of New York City, in large part newly arrived immigrants, lived in overcrowded tenements, many of whose rooms had no outside windows. Similar conditions prevailed in London, Berlin, Paris, Chicago, and other large cities. Infant mortality was high, and cholera epidemics broke out frequently. 19th-Century Urban Planning Modern urban planning owes its origin to the necessity for creating a more sanitary urban environment by demolishing the worst slums and controlling the quality of new construction. In England the Health of the Towns Act (1868) empowered municipalities to prescribe sanitary standards for housing and to issue a "closing order" when a dwelling was "unfit for human habitation," whereas the Public Health Act (1875) allowed towns to regulate new buildings and mandated the construction of water and sewer systems and the removal of refuse. Elsewhere in Europe new districts were planned on the urban fringe, replacing the now-obsolete fortifications, as in Vienna (1856) and Copenhagen (1865). Slums were cleared and broad avenues pierced through older districts, as in Paris, where Baron Georges Eugene \THaussmann\t launched (1848) an ambitious plan in the course of which more than 40% of the city's houses were torn down and replaced with new buildings, while new districts were laid out on the periphery and an extensive system of parks was created. In the United States, Pierre Charles L'ENFANT had laid out (1791) the new capital of Washington, D.C., on an enormous scale, with a rectangular street grid laid over a plan of radial avenues, with squares and circles at major intersections. Urban improvements had been limited to parks in the 19th century, but the European approach was popularized by Chicago's \TWorld's Columbian Exposition of\t 1893 whose dazzling white plaster buildings lining landscaped avenues fired the imagination of visitors with a vision of a more aesthetic and efficient urban environment. Plans, largely inspired by Haussmann's work in Paris, were prepared for a formal grouping of federal buildings in Washington, D.C. (1900), for San Francisco (1905), and for Chicago (1909). Many cities undertook to improve their water and sewer systems. Yet, despite improvements generated by the "City Beautiful" movement, city governments found imposing even minimal controls on private property politically difficult. The construction of unhealthy "old law" tenements was not outlawed in New York until 1901, and the new standards, prescribing an air shaft to ventilate inside rooms, were only marginally better. Only 22 cities had adopted height-restriction regulations by 1913; the first comprehensive zoning ordinance, specifying permitted uses as well as density of development, was not adopted in New York City until 1916. CONTEMPORARY URBAN PLANNING Effective urban planning comprises clear development objectives as well as the means to carry them out. Development objectives can vary greatly according to local conditions and the consensus that can be achieved on community goals. A city may choose to develop its unbuilt land, revitalize its downtown area, demolish its slums and replace them with new buildings, or any combination of these objectives. Its development objectives, usually combining social and physical aspects, are set forth in a comprehensive plan, which documents existing conditions, analyzes the causes of various shortcomings, and explores alternative solutions. By comparing the social, economic, and political costs and advantages of possible solutions, a preferred alternative can be selected and detailed into specific projects and programs. The implementation of a plan occurs over many years; its progress is a function of the city's ability to finance it as well as of the plan's political viability. The means at the city's disposal may range from the use of its normal regulatory powers to legislate for the health, safety, and general welfare of the population to direct intervention in the private market through tax incentives, the purchase of land and buildings by eminent domain, demolition of unsafe structures, and new construction. Zoning and Subdivision Zoning and subdivision regulations are the powers most commonly used to regulate private development. Zoning separates land uses that are deemed incompatible by dividing the city into districts where only structures for specified uses, such as single-family homes, apartments, retail, or industry, can be built. Minimum lot sizes, maximum building heights, and setbacks from property lines are commonly part of zoning. Subdivision regulations prescribe the site-planning standards to be used in housing developments. They specify road widths and turning radii, sidewalk dimensions, utilities and drainage, street lighting, and landscaping. Together with building and health codes, zoning and subdivision regulations can effectively control the quality of new construction. They have little influence on urban social problems, however, except insofar as they help determine the cost of new housing by specifying the amount of land required by a dwelling and the standard to which it is to be improved. Because the cost of improved land in a suburban subdivision typically accounts for 25% to 28% of the cost of the dwelling, variations in this amount will affect the cost of housing. Zoning has thus tended to result in socioeconomic stratification. In recent years large-lot suburban zoning ordinances have at times been declared unconstitutional by the courts as barriers to the mobility of lower-income families. Urban Renewal in the United States In the United States direct government intervention was the keystone of urban renewal. Intended in part to eliminate substandard housing, which was estimated to account for 19% of dwellings in cities of 100,000 or more population, the urban-renewal legislation that was adopted as part of the 1949 Housing Act postulated a cooperative process between the public and private sectors. Local governments purchased land containing a specified percentage of substandard structures, prepared a reuse plan, undertook necessary demolition, provided new streets and utilities, and sold the improved parcels to private developers willing to build in accordance with the renewal plan. The difference between the public costs of the project and the resale value of the land was shared between the federal and local governments, the federal share amounting to two-thirds of the net cost. More than 2,000 projects with an average area of 72 acres were initiated under this controversial program; its major shortcomings were the displacement of low-income families and a failure to construct as many low- and moderate-income housing units as had been demolished. New Towns Direct government intervention also takes place in the planning of \Tnew towns\t, whose origins go back to Ebenezer \THoward\t who, in his book Garden Cities of Tomorrow (1898), proposed to relieve the congestion of London by building self-contained communities (see \Tgarden city\t) on its periphery. In the United States, Howard's ideas were developed by Clarence Stein (1882-1975) and Henry \TWright\t in Radburn, N.J. (1928), and in the new towns, such as Greenbelt, Md. (1937), sponsored by the U.S. Resettlement Administration, which demonstrated the advantages of clustering housing in superblocks containing communal landscaped areas and of providing pedestrian and bicycle ways separate from vehicular traffic. Howard's ideas became most influential in England and continental Europe. After World War II the British government, through its newly created Ministry of Town and Country Planning, undertook an ambitious program of planned decentralization. Twenty-eight new towns, with target populations varying from 25,000 to 300,000, were built near congested industrial cities. In Europe new towns of similar magnitude are an integral part of the regional plans of Copenhagen, Helsinki, Stockholm, and Paris and have been used as well to promote the growth of underdeveloped regions. In Third World countries new towns have been constructed to promote economic development and to provide new capital cities. In the United States the magnitude of necessary public intervention has prevented the establishment of new towns from becoming official policy. The experience of other countries has shown that a large public investment was required to purchase the land and create the physical and social infrastructure. In addition, substantial financial incentives had to be offered to both housing developers and private industrial and commercial firms to induce them to locate in new towns, although some of these costs eventually could be recovered from land sales and taxes. The almost exclusively residential "new towns" that were privately developed in the United States starting in the 1960s--Reston, Va. (begun 1963), Columbia, Md. (begun 1962), Irvine, Calif. (begun 1960s)--are more akin to well-planned housing developments than to the self-contained European new towns. URBAN PLANNING SINCE 1960 Urban planning has evolved rapidly since the 1960s, extending its historical concern with the built environment to social and economic issues. The question is no longer whether planning is necessary, but rather how extensive planning should be. In the United States and in most Western industrialized countries, urban planning is now commonly understood to include the delivery of social services, the development of employment opportunities for the economically disadvantaged, the search for housing solutions that avoid the stigma of public housing projects, and the protection of the environment. More attention is also being paid to the participation of those affected by planning decisions through mandatory public hearings and community discussion of development alternatives. In the developing countries of the Third World a lack of investment capital and rates of urbanization two to three times higher than in the West, resulting from rapid population growth and migration from rural areas, have created problems of unprecedented magnitude. Typical urban planning priorities in the Third World include provision of a minimum sanitary shelter, when the average per-capita gross national product is $774, as opposed to $5,980 in the industrialized countries (1976); construction of sufficient educational facilities, when typically 44% of the population are children below the age of 15 and 50% or more of adults are illiterate; and creation of employment, when the rate of entry into the labor force is 2.5 times higher than in the West. In light of these conditions, planning has tended to be a centralized government function whose major preoccupation has been the allocation of scarce resources to projects furthering national economic development objectives. The protection of the environment and the aesthetic appearance of cities have understandably received less attention than in the wealthier nations. Francois C. D. Vigier Bibliography: Campbell, C. C., New Towns: Another Way to Live (1976); Clawson, Marion, and Hall, Peter, Planning and Urban Growth: An Anglo-American Comparison (1973); Eldredge, H. Wentworth, ed., Taming Megalopolis (1967); Galantry, Ervin Y., New Towns: Antiquity to the Present (1975); Hugo-Brunt, Michael, The History of City Planning (1972); Lynch, Kevin, The Image of the City (1960); Osborn, F. J., and Whittick, Arnold, New Towns (1977); Rasmussen, Steen Eiler, Towns and Buildings (1969); Real Estate Research Corporation, The Costs of Sprawl (1974); Reps, John W., The Making of Urban America (1965); Tunnard, Christopher, A World with a View: An Inquiry into the Nature of Scenic Values (1978); Tunnard, Christopher, and Pushkarev, Boris, Man-Made America: Chaos or Control? (1963).