Programs pursued as a means of improving the urban environment and achieving certain social and economic objectives. Evidence of urban planning can be found in the ruins of ancient cities, including orderly street systems and conduits for water and sewage. During the Renaissance, European city areas were consciously planned to achieve circulation of the populace and provide fortification against invasion. Such concepts were exported to the New World, where William Penn, in founding the city of Philadelphia, developed the standard gridiron plan—the laying out of streets and plots of land adaptable to rapid change in land use. Modern urban planning and redevelopment arose in response to the disorder and squalor of the slums created by the Industrial Revolution. The urban planner best known for his transformation of Paris was Georges-Eugène Haussmann. City planners imposed regulatory laws establishing standards for housing, sanitation, water supply, sewage, and public health conditions, and introduced parks and playgrounds into congested city neighbourhoods. In the 20th century, zoning—the regulation of building activity according to use and location—came to be a key tool for city planners. Seealso Pierre-Charles L'Enfant.
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Based upon the origins of urban planning from the roman (pre-dark ages) era, the current discipline revisits the synergy of the disciplines of urban planning, architecture and landscape architecture, varying upon from the interlectural strategic positioning from university to university.
Another key role of urban planning is urban renewal, and re-generation of inner cities by adapting urban planning methods to existing cities suffering from long-term infrastructural decay.
The development of technology, particularly the discovery of agriculture, before the beginning of recorded history facilitated larger populations than the very small communities of the Paleolithic, and may have compelled the development of stronger, more coercive governments at the same time. The pre-Classical and Classical ages saw a number of cities laid out according to fixed plans, though many tended to develop organically.
The cities of Harappa and Mohenjo-daro in the Indus Valley Civilization (in modern-day Pakistan and northwest India) are perhaps the earliest examples of deliberately planned and managed cities. The streets of these early cities were often paved and laid out at right angles in a grid pattern, with a hierarchy of streets from major boulevards to residential alleys. Archaeological evidence suggests that many Harrapan houses were laid out to protect from noise and enhance residential privacy; also, they often had their own water wells for probably both sanitary and ritual purposes. These ancient cities were unique in that they often had drainage systems, seemingly tied to a well-developed ideal of urban sanitation Ur, located near the Euphrates and Tigris rivers in modern day Iraq also had urban planning in later periods.
The Greek Hippodamus (c. 407 BC) is widely considered the father of city planning in the West, for his design of Miletus; Alexander commissioned him to lay out his new city of Alexandria, the grandest example of idealized urban planning of the Mediterranean world, where regularity was aided in large part by its level site near a mouth of the Nile.
The ancient Romans used a consolidated scheme for city planning, developed for military defense and civil convenience. The basic plan is a central forum with city services, surrounded by a compact rectilinear grid of streets and wrapped in a wall for defense. To reduce travel times, two diagonal streets cross the square grid corner-to-corner, passing through the central square. A river usually flowed through the city, to provide water, transport, and sewage disposal. Many European towns, such as Turin, still preserve the essence of these schemes. The Romans had a very logical way of designing their cities. They laid out the streets at right angles, in the form of a square grid. All the roads were equal in width and length, except for two. These two roads formed the center of the grid and intersected in the middle. One went East/West, the other North/South. They were slightly wider than the others. All roads were made of carefully fitted stones and smaller hard packed stones. Bridges were also constructed where needed. Each square marked by four roads was called an insula, which was the Roman equivalent of modern city blocks. Each insula was square, with the land within each insula being divided up. As the city developed, each insula would eventually be filled with buildings of various shapes and sizes and would be crisscrossed with back roads and alleys. Most insulae were given to the first settlers of a budding new Roman city, but each person had to pay for the construction of their own house. The city was surrounded by a wall to protect the city from invaders and other enemies, and to mark the city limits. Areas outside of the city limits were left open as farmland. At the end of each main road, there would be a large gateway with watchtowers. A portcullis covered the opening when the city was under siege, and additional watchtowers were constructed around the rest of the city’s wall. A water aqueduct was built outside of the city's walls.
The collapse of Roman civilization saw the end of their urban planning, among many other arts. Urban development in the Middle Ages, characteristically focused on a fortress, a fortified abbey, or a (sometimes abandoned) Roman nucleus, occurred "like the annular rings of a tree whether in an extended village or the center of a larger city. Since the new center was often on high, defensible ground, the city plan took on an organic character, following the irregularities of elevation contours like the shapes that result from agricultural terracing.
The ideal of wide streets and orderly cities was not lost, however. A few medieval cities were admired for their wide thoroughfares and other orderly arrangements, but the juridical chaos of medieval cities (where the administration of streets was sometimes hereditary with various noble families), and the characteristic tenacity of medieval Europeans in legal matters, prevented frequent or large-scale urban planning until the Renaissance and the enormous strengthening of all central governments, from city-states to the kings of France, characteristic of that epoch. Florence was an early model of the new urban planning, which rearranged itself into a star-shaped layout adapted from the new star fort, designed to resist cannon fire. This model was widely imitated, reflecting the enormous cultural power of Florence in this age; "[t]he Renaissance was hypnotized by one city type which for a century and a half— from Filarete to Scamozzi— was impressed upon utopian schemes: this is the star-shaped city Radial streets extend outward from a defined center of military, communal or spiritual power. Only in ideal cities did a centrally-planned structure stand at the heart, as in Raphael's Sposalizio of 1504 (illustration); as built, the unique example of a rationally-planned quattrocento new city center, that of Vigevano, 1493-95, resembles a closed space instead, surrounded by arcading. Filarete's ideal city, building on hints in Leone Battista Alberti's De re aedificatoria, was named "Sforzinda" in compliment to his patron; its twelve-pointed shape, circumscribable by a "perfect" Pythagorean figure, the circle, takes no heed of its undulating terrain in Filarete's manuscript. And, all this occurred in the cities, but ordinarily not in the industrial suburbs characteristic of this era (see Bradel, The Structures of Everyday Life), which remained disorderly and characterized by crowded conditions and organic growth. In the 1990s, the University of Kentucky voted the Italian town of Todi as ideal city and "most livable town in the world", the place where man and nature, history and tradition come together to create a site of excellence. In Italy, other examples of ideal cities planned according to scientific methods, are: Urbino, Pienza, Ferrara, San Giovanni Valdarno, San Lorenzo Nuovo.
Many cities in Central American civilizations also engineered urban planning in their cities including sewage systems and running water. In Mexico, Tenochtitlan, was the capital of the Aztec empire, built on an island in Lake Texcoco in what is now the Federal District in central Mexico. At its height, Tenochtitlan was one of the largest cities in the world, with close to 250,000 inhabitants.
Shibam in Yemen features over 500 tower houses, each one rising 5 to 11 storeys high, with each floor being an apartment occupied by a single family. The city has some of the tallest mudbrick houses in the world, with some of them being over 100 feet high (over 30 meters).
In developed countries (Western Europe, North America, Japan and Australasia), planning and architecture can be said to have gone through various stages of general consensus in the last 200 years. Firstly, there was the industrialised city of the 19th century, where control of building was largely held by businesses and the wealthy elite. Around 1900, there began to be a movement for providing citizens, especially factory workers, with healthier environments. The concept of garden cities arose and several model towns were built, such as Letchworth and Welwyn Garden City, the world's first garden cities, in Hertfordshire, UK. However, these were principally small scale in size, typically dealing with only a few thousand residents.
It wasn't until the 1920s that modernism began to surface. Based on the ideas of Le Corbusier and utilising new skyscraper building techniques, the modernist city stood for the elimination of disorder, congestion and the small scale, replacing them instead with preplanned and widely spaced freeways and tower blocks set within gardens. There were plans for large scale rebuilding of cities, such as the Plan Voisin (based on Le Corbusier's Ville Contemporaine), which proposed clearing and rebuilding most of central Paris. No large-scale plans were implemented until after World War II however. Throughout the late 1940s and 1950s, housing shortages caused by war destruction led many cities around the world to build substantial amounts of government-subsidized housing blocks. Planners at the time used the opportunity to implement the modernist ideal of towers surrounded by gardens. The most prominent example of an entire modernist city is Brasilia, constructed between 1956 and 1960 in Brazil.
By the late 1960s and early 1970s, many planners were coming to realize that the imposition of modernist clean lines and a lack of human scale also tended to sap vitality from the community. This was expressed in high crime and social problems within many of these planned neighbourhoods. Modernism can be said to have ended in the 1970s when the construction of the cheap, uniform tower blocks ended in many countries, such as Britain and France. Since then many have been demolished and in their way more conventional housing has been built. Rather than attempting to eliminate all disorder, planning now concentrates on individualism and diversity in society and the economy. This is the post-modernist era.
Minimally-planned cities still exist. Houston is an example of a large city (with a metropolitan population of 5.5 million) in a developed country, without a comprehensive zoning ordinance. Houston does, however, have many of the land use restrictions covered by traditional zoning regulations, such as restrictions on development density and parking requirements, even though specific land uses are not regulated. Moreover, private-sector developers in Houston have used subdivision covenants and deed restrictions effectively to create the same kinds of land use restrictions found in most municipal zoning laws. Houston voters have rejected proposals for a comprehensive zoning ordinance three times since 1948. Even without zoning in its traditional sense, metropolitan Houston displays similar land use patterns at the macro scale to regions comparable in age and population that do have zoning, such as Dallas. This suggests that factors outside the regulatory environment, such as the provision of urban infrastructure and methods of financing development, may play as big of a role in urban development as municipal zoning.
Stephen Wheeler, in his 1998 article, suggests a definition for sustainable urban development to be as "development that improves the long-term social and ecological health of cities and towns. He goes on to suggest a framework that might help all to better understand what a 'sustainable' city might look like. These include compact, efficient land use; less automobile use yet with better access; efficient resource use, less pollution and waste; the restoration of natural systems; good housing and living environments; a healthy social ecology; sustainable economics; community participation and involvement; and preservation of local culture and wisdom. The challenge facing today's urban planners lies in the implementation of targeted policies and programs, and the need to modify existing urban and regional institutions to achieve the goals of sustainability.
In developed countries, there has been a backlash against excessive man-made clutter in the visual environment, such as signposts, signs, and hoardings. Other issues that generate strong debate amongst urban designers are tensions between peripheral growth, increased housing density and planned new settlements. There are also unending debates about the benefits of mixing tenures and land uses, versus the benefits of distinguishing geographic zones where different uses predominate. Regardless, all successful urban planning considers urban character, local identity, respect for heritage, pedestrians, traffic, utilities and natural hazards.
Planners are important in managing the growth of cities, applying tools like zoning to manage the uses of land, and growth management to manage the pace of development. When examined historically, many of the cities now thought to be most beautiful are the result of dense, long lasting systems of prohibitions and guidance about building sizes, uses and features. These allowed substantial freedoms, yet enforce styles, safety, and often materials in practical ways. Many conventional planning techniques are being repackaged using the contemporary term smart growth.
There are some cities that have been planned from conception, and while the results often don't turn out quite as planned, evidence of the initial plan often remains. (See List of planned cities)
Historically within the Middle East, Europe and the rest of the Old World, settlements were located on higher ground (for defense) and close to fresh water sources. Cities have often grown onto coastal and flood plains at risk of floods and storm surges. Urban planners must consider these threats. If the dangers can be localised then the affected regions can be made into parkland or Greenbelt, often with the added benefit of open space provision.
Extreme weather, flood, or other emergencies can often be greatly mitigated with secure emergency evacuation routes and emergency operations centres. These are relatively inexpensive and unintrusive, and many consider them a reasonable precaution for any urban space. Many cities will also have planned, built safety features, such as levees, retaining walls, and shelters.
In recent years, practitioners have also been expected to maximize the accessibility of an area to people with different abilities, practicing the notion of "inclusive design," to anticipate criminal behaviour and consequently to "design-out crime" and to consider "traffic calming" or "pedestrianisation" as ways of making urban life more pleasant.
City planning tries to control criminality with structures designed from theories such as socio-architecture or environmental determinism. These theories say that an urban environment can influence individuals' obedience to social rules. The theories often say that psychological pressure develops in more densely developed, unadorned areas. This stress causes some crimes and some use of illegal drugs. The antidote is usually more individual space and better, more beautiful design in place of functionalism.
Oscar Newman’s defensible space theory cites the modernist housing projects of the 1960s as an example of environmental determinism, where large blocks of flats are surrounded by shared and disassociated public areas, which are hard for residents to identify with. As those on lower incomes cannot hire others to maintain public space such as security guards or grounds keepers, and because no individual feels personally responsible, there was a general deterioration of public space leading to a sense of alienation and social disorder.
Jane Jacobs is another notable environmental determinist and is associated with the "eyes on the street" concept. By improving ‘natural surveillance’ of shared land and facilities of nearby residents by literally increasing the number of people who can see it, and increasing the familiarity of residents, as a collective, residents can more easily detect undesirable or criminal behaviour.
The "broken-windows" theory argues that small indicators of neglect, such as broken windows and unkempt lawns, promote a feeling that an area is in a state of decay. Anticipating decay, people likewise fail to maintain their own properties. The theory suggests that abandonment causes crime, rather than crime causing abandonment.
Some planning methods might help an elite group to control ordinary citizens. Haussmann's renovation of Paris created a system of wide boulevards which prevented the construction of barricades in the streets and eased the movement of military troops. In Rome, the Fascists in the 1930s created ex novo many new suburbs in order to concentrate criminals and poorer classes away from the elegant town.
Other social theories point out that in Britain and most countries since the 18th century, the transformation of societies from rural agriculture to industry caused a difficult adaptation to urban living. These theories emphasize that many planning policies ignore personal tensions, forcing individuals to live in a condition of perpetual extraneity to their cities. Many people therefore lack the comfort of feeling "at home" when at home. Often these theorists seek a reconsideration of commonly used "standards" that rationalize the outcomes of a free (relatively unregulated) market.
The rapid urbanization of the last century has resulted in a significant amount of slum habitation in the major cities of the world, particularly in developing countries. There is significant demand for planning resources and strategies to address the issues that arise from slum development. Many planning theorists and practitioners are calling for increased attention and resources in this area, particularly the Commonwealth Association of Planners. When urban planners give their attention to slums, one also has to pay attention to the racial make-up of that area to ensure that racial steering does not occur.
The issue of slum habitation has often been resolved via a simple policy of clearance. However, more creative solutions are beginning to emerge such as Nairobi's "Camp of Fire" program, where established slum-dwellers have promised to build proper houses, schools, and community centers without any government money, in return for land they have been illegally squatting on for 30 years. The "Camp of Fire" program is one of many similar projects initiated by Slum Dwellers International, which has programs in Africa, Asia, and South America.
Urban decay is a process by which a city, or a part of a city, falls into a state of disrepair and neglect. It is characterized by depopulation, economic restructuring, property abandonment, high unemployment, fragmented families, political disenfranchisement, crime, and desolate urban landscapes.
During the 1970s and 1980s, urban decay was often associated with central areas of cities in North America and parts of Europe. During this time period, major changes in global economies, demographics, transportation, and government policies created conditions that fostered urban decay. Many planners spoke of "white flight" during this time. This pattern was different than the pattern of "outlying slums" and "suburban ghettos" found in many cities outside of North America and Western Europe, where central urban areas actually had higher real estate vales. Starting in the 1990s, many of the central urban areas in North America have been experiencing a reversal of the urban decay of previous decades, with rising real estate values, smarter development, demolition of obsolete social housing areas and a wider variety of housing choices..
Areas devastated by war or invasion represent a unique challenge to urban planners. Buildings, roads, services and basic infrastructure like power, water and sewerage are often severely compromised and need to be evaluated to determine what can be salvaged for re-incorporation. There is also the problem of the existing population, and what needs they may have. Historic, religious or social centers also need to be preserved and re-integrated into the new city plan. A prime example of this is the capital city of Kabul, Afghanistan, which, after decades of civil war and occupation, has regions that have literally been reduced to rubble and desolation. Despite this, the indigenous population continues to live in the area, constructing makeshift homes and shops out of whatever can be salvaged. Any reconstruction plan proposed, such as Hisham Ashkouri's City of Light Development, needs to be sensitive to the needs of this community and its existing culture, businesses and needs.
Urban Reconstruction Development plans must also work with government agencies as well as private interests to develop workable designs.
Transport within urbanized areas presents unique problems. The density of an urban environment can create significant levels of road traffic, which can impact businesses and increase pollution. Parking space is another concern, requiring the construction of large parking garages in high density areas which could be better used for other development.
Good planning uses transit oriented development, which attempts to place higher densities of jobs or residents near high-volume transportation. For example, some cities permit commerce and multi-story apartment buildings only within one block of train stations and multilane boulevards, and accept single-family dwellings and parks farther away.
Floor area ratio is often used to measure density. This is the floor area of buildings divided by the land area. Ratios below 1.5 could be considered low density, and plot ratios above five very high density. Most exurbs are below two, while most city centres are well above five. Walk-up apartments with basement garages can easily achieve a density of three. Skyscrapers easily achieve densities of thirty or more.
City authorities may try to encourage lower densities to reduce infrastructure costs, though some observers note that low densities may not accommodate enough population to provide adequate demand or funding for that infrastructure. In the UK, recent years have seen a concerted effort to increase the density of residential development in order to better achieve sustainable development. Increasing development density has the advantage of making mass transport systems, district heating and other community facilities (schools, health centres, etc) more viable. However critics of this approach dub the densification of development as 'town cramming' and claim that it lowers quality of life and restricts market-led choice.
Problems can often occur at residential densities between about two and five. These densities can cause traffic jams for automobiles, yet are too low to be commercially served by trains or light rail systems. The conventional solution is to use buses, but these and light rail systems may fail where automobiles and excess road network capacity are both available, achieving less than 1% ridership.
The Lewis-Mogridge Position claims that increasing road space is not an effective way of relieving traffic jams as latent or induced demand invariably emerges to restore a socially-tolerable level of congestion.
In some countries, declining satisfaction with the urban environment is held to blame for continuing migration to smaller towns and rural areas (so-called urban exodus). Successful urban planning supported Regional planning can bring benefits to a much larger hinterland or city region and help to reduce both congestion along transport routes and the wastage of energy implied by excessive commuting.
In most advanced urban or village planning models, local context is critical. In many, gardening and other outdoor activities assumes a central role in the daily life of citizens. Environmental planners are focusing on smaller systems of resource extraction, energy production and waste disposal. There is even a practice known as Arcology, which seeks to unify the fields of ecology and architecture, using principles of landscape architecture to achieve a harmonious environment for all living things. On a small scale, the eco-village theory has become popular, as it emphasizes a traditional 100-140 person scale for communities.
An urban planner is likely to use a number of quantitative tools to forecast impacts of development on the environmental, including roadway air dispersion models to predict air quality impacts of urban highways and roadway noise models to predict noise pollution effects of urban highways. As early as the 1960s, noise pollution was addressed in the design of urban highways as well as noise barriers. The Phase I Environmental Site Assessment can be an important tool to the urban planner by identifying early in the planning process any geographic areas or parcels which have toxic constraints.
In urban planning, sound is usually measured as a source of pollution. Another perspective on urban sounds is developed in Soundscape studies emphasising that sound aesthetics involves more than noise abatement and decibel measurements. Hedfors coined 'Sonotope' as a useful concept in urban planning to relate typical sounds to a specific place.
The traditional planning process focused on top-down processes where the urban planner created the plans. The planner is usually skilled in either surveying, engineering or architecture, bringing to the town planning process ideals based around these disciplines. They typically worked for national or local governments.
Changes to the planning process over past decades have witnessed the metamorphosis of the role of the urban planner in the planning process. More citizens calling for democratic planning processes have played a huge role in allowing the public to make important decisions as part of the planning process. Community organizers and social workers are now very involved in planning from the grassroots level.
Developers too have played huge roles in influencing the way development occurs, particularly through project-based planning. Many recent developments were results of large and small-scale developers who purchased land, designed the district and constructed the development from scratch. The Melbourne Docklands, for example, was largely an initiative pushed by private developers who sought to redevelop the waterfront into a high-end residential and commercial district.
Recent theories of urban planning, espoused, for example by Salingaros see the city as a adaptive system that grows according to process similar to those of plants. They say that urban planning should thus take its cues from such natural processes.