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In land use planning, urban open space is open space areas for "parks", "green spaces", and other open areas. The landscape of urban open spaces can range from playing fields to highly maintained environments to relatively natural landscapes. They are commonly open to public access, however, urban open spaces may be privately owned. Areas outside of city boundaries, such as state and national parks as well as open space in the countryside, are not considered urban open space. Streets, piazzas, plazas and urban squares are not always defined as urban open space in land use planning.
The term "urban open space" can describe many types of open areas. One definition holds that, "As the counterpart of development, urban open space is a natural and cultural resource, synonymous with neither 'unused land' nor 'park and recreation areas." Another is "Open space is land and/or water area with its surface open to the sky, consciously acquired or publicly regulated to serve conservation and urban shaping function in addition to providing recreational opportunities." In almost all instances, the space referred to by the term is, in fact, green space. However, there are examples of urban green space which, though not publicly owned/regulated, are still considered urban open space.
Generally considered open to the public, urban open spaces are sometimes privately owned. Some examples of such places include higher education campuses, neighborhood/community parks/gardens, and institutional or corporate grounds. These areas still function to provide "aesthetic and psychological relief from urban development". Nevertheless, most commonly the term is used to reference spaces that are public and "green".
The benefits that urban open space provides to citizens can be broken into three basic forms; recreation, ecology, and aesthetic value.
Urban open space is often appreciated for the recreational opportunities it provides. Recreation in urban open space may include active recreation (such as organized sports and individual exercise) or passive recreation, which may simply entail being in the open space. Time spent in an urban open space for recreation offers a reprieve from the urban environment.
The conservation of nature in an urban environment has direct impact on people for another reason as well. A Toronto civic affairs bulletin entitled Urban Open Space: Luxury or Necessity makes the claim that "popular awareness of the balance of nature, of natural processes and of man’s place in and effect on nature – i.e., "ecological awareness" – is important. As human live more and more in man-made surroundings – i.e., cities – he risks harming himself by building and acting in ignorance of natural processes." Beyond this man-nature benefit, urban open spaces also serve as islands of nature, promoting biodiversity and providing a home for natural species in environments that are otherwise uninhabitable due to city development.
The aesthetic value of urban open spaces is self-evident. People enjoy viewing nature, especially when it is otherwise extensively deprived, as is the case in urban environments. Therefore, open space offers the value of "substituting gray infrastructure."
The value of urban open space can also be considered with regards to the specific functions it provides. For example, the Bureau of Municipal Research in Toronto lists these functions as the nature function, urban design function, economic function, social retreat function, and outdoor recreation function. Another study categorizes the values open space offers from a sociological viewpoint, listing: civic and social capital, cultural expression, economic development, education, green infrastructure, public health, recreation, and urban form. These studies reiterate the same core benefits of urban open spaces and none of the options create any inconsistencies with the others.
Additional beneficial aspects of urban open space can be factored into how valuable it is compared to other urban development. One study categorizes these measures of value into six groups: utility, function, contemplative, aesthetic, recreational, and ecological. These categories account for the value an urban open space holds to the development of the city in addition to just those things citizens consciously appreciate. For example, the "function value" of an open space accounts for the advantages an urban open space may provide in controlling runoff. The final three values listed, aesthetic, recreational, and ecological, are essentially the same as the values that make urban open spaces consciously valuable to citizens. Of course, there are several different ways to organize and refer to the merit of open space in urban planning.
Significant research supports the notion that urban open spaces offer health benefits to city residents through exposure to a natural environment. It has been unambiguously shown that there is a strong association between the enjoyment of nature and the health of a city population in general. Studies have examined several aspects of this association and also specific impacts on distinct demographic groups. Most have been reviewed and listed in a comprehensive analysis by the Health Council of the Netherlands
A large epidemiological study  in Britain looked at mortality and morbidity among three income levels in relation to their access to green open space. The study examined about 360,000 deaths in a population of about 41 million. While it confirmed that wealthier individuals were generally healthier than those with lower incomes, it made another remarkable discovery: That all groups irrespective of income showed an improvement in health in proportion to their access to green space and that the differences in health status between income groups, who had equivalent access to progressively more green space, shrank favouring the lowest socio-economic group with the highest morbidity.In simple terms, everyone benefited but the lowest income group benefited the most. (see chart). These striking results based on an exceptionally large sample confirm unambiguously the health-related effects of green space and suggest its importance as an element in neighbourhood layouts. Not only would it reduce health disparities between incomes but it would also promote general health and well-being.
A second epidemiological study in the Netherlandsexamined the health of 17,000 people in relationship to the presence of green space in their surroundings. It found that residents of neighbourhoods with abundant green space were, on average, healthier. This correlation was clearly evident in the general population but it was more pronounced among seniors, housewives and low-income people. Also significant was the correlation between health and the total amount of green space, which, in some cases, was located at a distance of 1-3 km from home.
A third study took place in Tokyo,  which is known for its very high building density. This was a longitudinal study that followed a group of 3,000, 70-year old citizens over five years. The presence of relatively plentiful green space in a neighbourhood correlated with a lower mortality risk. This correlation was stronger in a sub-sample of elderly people with few physical disabilities.
Other research looked at specific demographic groups such as age, occupation, socioeconomic status and unusual health conditions or symptoms. Though these studies vary in their degree of scientific rigour, they all point to the potential benefits of nearby nature. For example: • Convincing evidence suggests that nature has a positive effect on recovery from stress and attention fatigue. For example people in highly stressful occupations such as caregivers or hospital nurses can shed much of their stress by being or walking in natural settings. This detente, evidently, can occur even when the exposure to nature is brief. • Similarly, evidence shows that nature has a positive impact on mood, concentration, mental fatigue, self-discipline and physiological stress. • Likewise, results that show faster recovery rates for hospital patients, who have a view of nature through their window, can be attributed to stress reduction, in the absence of other explanatory mechanisms. • Parents of children suffering from Attention Deficit Disorder, report improvement and fewer attention problems when the area of play is in natural settings • Green spaces may enhance the potential of creating and sustaining community interaction and networks
Last Child in the Woods speaks of the positive effects nature in general has on children, even when experienced in small islands of green within a city. Urban open spaces offer citizens relief from the strains of urban environments and everyday demands. That respite can come in the form of a walk or run, time spent sitting or reading, watching the birds, essentially any time spent in the natural environment the open space offers. Research shows that when open spaces are attractive and accessible, people are more likely to engage in physical activity, which has obvious inherent health benefits. Accessibility has been shown to increase open space use, which drops dramatically for distances longer than a five-minute walk (about 400 m). Neighbourhood layouts such as the Oglethorpe Plan for Savannah, GA or the contemporary Fused Grid achieve high degree of accessibility.
Public recreation parks are multi-use, but recent advances in best practices has prompted many cities to move away from old-fashioned and biologically impoverished "urban savannah" designs, to mosaic environments, which allow full recreational use but maintain higher levels of biodiversity and hence deliver greater benefits to human well-being. A recent study in Sheffield, UK, found that the psychological benefits gained by visitors to urban green spaces increased with their biodiversity, indicating that 'green' alone is not sufficient; the quality of that green is important in delivering the health benefits.
The environment of an urban open space significantly influences how that space is perceived and used. Some green spaces maintain a natural environment with a native and self-sustaining ecosystem. Depending on factors such as the location of the city and the location of the space within the city, this natural open space may be a grassy field, woodland, or something aquatic such as a stream, swamp, pond or lake. Other areas may be more heavily influenced by its purpose and use. Examples of open space that would match this description are playing fields, gardens, or imposed ecosystems.
Species of flora and fauna commonly found in urban open space may include species that have adapted to city life as well as species not typical in the conventional urban environment because of significantly different ecosystems that comprise urban open spaces. Species most often able to co-exist with man in an urban setting are usually those that "are able to reproduce rapidly and to take advantage of transitory conditions or to evolve varieties suited to the urban situation". Therefore, larger urban open spaces, especially those with various types of environments, are more likely to support a diverse ecosystem. Depending on the type of open space, species may be either exotic and native producing a corresponding ecosystem. Often, large urban open spaces that rely on a natural local ecosystem experience greater success in terms of maintaining a balanced biodiversity, so long as the areas are "established and managed primarily to benefit natural wildlife populations in order that they may function as regional reservoirs."
The basis for many urban open spaces seen today across Europe and the West began its process of development in London in the 17th and 18th centuries. What would eventually become urban open green space began as paved public plazas. Though they were intended to be open to the public, these spaces began to be re-designated as private parks around the late eighteenth century. It was during this period that the areas became pockets of green in the urban environment, commonly modelled after the natural wild of the countryside.
The first parks to reverse the trend of privatization and again be opened to the public were England’s royal parks in the nineteenth century. This was done in response to the extensive and unexpected population movement from the country into cities. As a result, "the need for open space was socially and politically pressing… The problems, to which the provision of parks was expected to offer some relief, were easy to describe: overcrowding, poverty, squalor, ill-health, lack of morals and morale, and so on". Such sentiments again received significant popular support during the "City Beautiful" movement in America during the 1890s and 1900s. Both trends focused on providing the public an opportunity to receive all of the perceived health and lifestyle benefits of having access to open space within urban environments.
Segmentation of urban open spaces was particularly prominent in America during the twentieth century. Since the late 1800s romantic park systems, open space designers have been concerned with guiding, containing or separating urban growth, distributing recreation, and/or producing scenic amenity, mostly within the framework of geometric abstractions." Such segmentation was especially prominent in the 1990s, when urban open spaces took a path similar to that of parks, following the modernization trend of segmentation and specialization of areas. As modernity stressed "increased efficiency, quantifiablity, predictability, and control… In concert with the additional social divisions" (Young 1995), open spaces grew more specific in purpose. Perhaps this increase in division of social classes’ use of open space, demonstrated by the segmentation of the spaces, displays a situation similar to the privatization of London parks in the eighteenth century, which displayed a desire to make classes more distinct.
Today, places like Scandinavia, which do not have a significant history of outdoor recreation and gathering places, are seeing a proliferation of urban open spaces and adopting a lifestyle supported by the extra urban breathing room. An example of this can be seen in Copenhagen where an area closed to car traffic in 1962 developed, in just a few decades, a culture of public political gatherings and outdoor cafes emerged. Not only is appreciation for and use of urban open spaces flourishing in locations that historically lacked such traditions, the number of urban open spaces is increasing rapidly as well.
Properties near urban open space tend to have a higher value. One study was able to demonstrate that, “a pleasant view can lead to a considerable increase in house price, particularly if the house overlooks water (8–10%) or open space (6–12%).” When it comes to proximity to the park edge, while there is a premium attached to apartments in close vicinity to the park, a negative premium is attached to this attribute for single family houses, which may be due to the potential negative externalities that may surround parks, particularly in the evenings.
Urban open space is under strong pressure. Due to increasing urbanization, combined with a spatial planning policy of densification, more people face the prospect of living in less green residential environments, especially people from low economic strata. This may lead to environmental injustice with regard to the distribution of (access) to public green space.
One study, which compared public open spaces between high socioeconomic neighborhoods and low socioeconomic neighborhoods, found that urban open space in the highest socioeconomic neighborhoods had more amenities (e.g. picnic tables, drink fountains and toilets) than open spaces in lower socioeconomic neighborhoods. Urban open spaces in higher socioeconomic neighborhoods were more likely to have trees that provided shade, a water feature (e.g. pond, lake and creek), walking and cycling paths, lighting, signage regarding dog access and signage restricting other activities as well.