| Rapid urbanization brings construction land radical expansion. The agricultural production land, mountain land, forest land, water area and other natural ecological land are facing to be invaded worse and worse. The urban ecological environment, recreational space and public space are being under compressed pressure. To meet the public demands of ecological environment, recreation, etc, the natural ecological land outside of city should be protected strictly. In addition, the scale and layout of public and accessory green space in construction land are very important. Production land, natural ecological land, public green space etc are just elements of open space. The researches of open space have also been the focus of domestic and foreign scholars' study.Based on making clear open space connotation and researching object in this article, research stage, the main research aspects and the theory about open space at home and abroad are reviewed. The characteristics, shortcomings and inspirations of open space study are summarized. The result of study on the evolution and development course of open space indicates some regular pattern. Squares are made as the center of open space in foreign countries. Natural elements are paid more and more attention to gradually. In our country, the ideas of shan-shui ideology are formed in development of open space.Since reform and opening-up, urban construction has achieved great development in China. With the characteristics of ancient capitals and garden city, Nanjing city is getting quick expansion. This paper chooses Nanjing city as typical cases. Based on remote sensing data, the data of land use, social economic data and literature material, using GIS spatial analysis, circling and fan analysis, ESDA method, landscape index analysis, structural equation and factor analysis methods etc, the open space and its types patterns of status in the year of 2006 and evolution from 1979 to 2006 are analysed. The mechanism of open space patterns formation and evolution are concluded.The research of evolution and its mechanism of urban open space pattern could enrich theoretical research foundation of garden city, ecological city and sustainable development. In practice, the study could provide the scientific basis for early warning of urban ecological environment deterioration, the judgment of open space shortage and urban open space planning. The construction of infrastructure and public welfare could help to guide urban layout and optimize space structure of city. According to impact factors and dynamic mechanism of open space pattern evolution, the study maybe provide the strategy of relieving urban unrestricted trend of spreading and ensure the healthy development of the city effectively.The analysis of current situation of the open space shows that the open space in the central city is mainly made up of green space. There are great amount and form differences in different districts in the city. Traffic accessibility in different regions causes the unbalance of service convenience. Moreover, comparing to schools, hospitals and other public facilities, open space is not key factor when citizens choose the living environment.The evolution analysis of the four time sections suggest that the area of public green space, accessory green space and the square are increasing constantly. However, the production green space, ecological buffer green space and water area are greatly reducing. Open space also appears a decrease trend from 1979 to 2006. Landscape index analysis also indicates that the member of patch, density of patch, average patch area of open space are decreasing constantly. Distributing of patches decentralize in whole. The mean shape index of open space patches are increasing. With the increasing of human amount and the planning influence deepening, open space patterns transform from self-constructing to 'be-constructed'. All types of open space appear certain evolution mode. The changes of scale and layout also make great changes of the public using the open space access. In Nanjing city, the accessibility level of internal open space is low in the early period. With the increase of public green space in the central city internal and the decrease of production green space and waters in its periphery, poor accessibility regions also have a trend of spread. However the fringes in the central city with more open space and convenient traffic condition have better accessibility levels.The evolution of open space pattern is constrained by the urban natural environmental, affected by the policy adjustment of national or local, and supported by social and economic development. Urban expansion force is the direct driving force of evolution. Economic development and increased investment are the original motivation Industrial restructuring is the lifting force. Road construction is an important guiding force. Social demand is also an important driving force of open space pattern evolution. The problems which include the poor balance, the weak system integrity, and fast reduction of open space patterns in the central city of Nanjing in the evolution process are revealed. According to urban green space system planning and weighted voronoi method, optimizing control countermeasures which including land use, proposed adjustment, layout optimization, population evacuation, strengthening green ring and belt construction, making full use of affiliated green space etc were put forward.The innovation of this paper focuses on the following two aspects. First, using RS, GIS and mathematical modeling methods, the situation and evolution characteristics of the urban internal space open space and its internal are researched systematically. There are development and extension to the urban space and open space research in a sense. Second, using weighted voronoi method, with fully consideration of population distribution open space area, traffic conditions, problems of urban open space layout are analysed. It provides a method to optimize the open space patterns. |
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