| Urbanization is the result of human socio-economic and cultural development, and it is the trend of social development and the sign of civilization. However, the rapid development of modern industrial civilization and urbanization process have caused many problems, such as the population increase, environmental pollution, ecological damage, and brought a large number of urban ecological security issues. As the important reflection of sustainable development of urban ecological system and urban ecological environment supporting capacity, it is great significance to research the internal relations and mechanism of the urban ecological security comprehensively and objectively.To be one of major cities in the central and western China, Xi'an is not only the political, economic and cultural center of Shaanxi Province, but also links the eastern and western regions of China's transportation and communications. During the process of its socio-economic rapid development and the development of industrialization and urbanization, it inevitably produced a lot of problems.In this paper, the author selected the city of Xi'an as a study area. First of all, the author summed up the various existing methods of ecological security evaluation and analyzed the advantages and disadvantages of each method. Then considered the specific circumstances of the study area and the existing data and technology, the author chose the right model of urban ecological security evaluation and eventually built an index system with 26 specific indicators evaluation of the urban ecological security evaluation, attempted to explore the issues of urban ecological security in the research area. Finally, some conclusions are obtained in the paper as follows:(1) ecological security evaluationThrough the indicators data processing of standardization and weight assignment, and the grid overlay computing of different layers, the paper finally attained the distribution of urban ecological security in the year of 1991,1996,2001,2005. The value of ecological security is between 40.78-53.16 in 1991, 41.78-56.02 in 1996, and in the year of 2001 and 2005, the value is between 46.37-59.51 and 48.74-65.77. From the bottom value of ecological security, it can be seen that the value of ecological security of Xi'an is rising on the whole between 1991-2005, but in different regions it showed different changes, and also there's a clear differences of regional distribution in the same year.This paper classified the value of urban ecological security to four grades of unsafety, critical safety, safety and ideal safety, and made a series of maps of ecological security in 1991,1996,2001,2005, which directly reflects 15 years ecological security situation changes from the period of 8th to 11th Five-Year Plan in Xi'an. In addition, the article analyzed the trends of ecological security changes on the study area. It can be found that in the Districts of Yanta, Baqiao, Weiyang, the situation of ecological security in Yanta is best over the years, followed by Weiyang, the end is Baqiao. The Xincheng District is a little better than Beilin, and Lianhu District relatively poor in the urban areas.Combined with the ecological security evaluation results of the study area, the article analyzed the evaluation index of urban ecological security. With the features of Xi'an and evaluation result, and the urban ecological security issues exhibited in the process of urbanization in the city of Xi'an, the article put forward six specific aspects of methods for the city's ecological construction and protection based on some experiences of other cities from home and abroad, which giving some references to relevant departments for ecological security control.(2) ecological security information systemAs a new technology began in 1960's, Geographic Information System makes the computer graphics and database management, geospatial information and related properties into an organic combination. According to the actual needs, the result will be illustrated in output, and with its unique ability of spatial analysis and visualization, it could provide all kinds of decision-making function.Based on the comparative analysis of several major GIS software secondary development methods, the article analyzed the advantage of component-based GIS development methods and introduced the ArcObjects development component of ESRI's ArcGIS products. Then integrated the ArcObjects development components into the Visual C++ development environment, the author designed and developed Xi'an ecological security information system, and realized some functions, such as the data query and update of the urban ecological security indicators, the index system settings and ecological security classification and thematic maps control functions.As for the research of urban ecological security in China have not formed a complete theoretical system and mature technology, and during the former research, the farming-pastoral zone and extremely fragile ecological areas or the resources based cities were chosen for the research region mostly. The innovations of the study are the following: (1) Select the Midwest large city of China- Xi'an as a study area for urban ecological security evaluation, and try to create suitable and scientific evaluation index system for the study area. Further more, select key factors to evaluate for the purpose of reflecting the situation of urban ecological security and enriching the urban ecological security case study. In the end, the research will provide some practical references and useful ideas for the development of urban ecological security theory and technology. (2) Use Visual C + + integrated development environment, with ArcObjects development components of the secondary development software of GIS, try to create Xi'an ecological security information system, extending the applications of Geographic Information System and providing further analysis of the cause and mechanism about the problems of urban ecological security.Due to my limited ability and the consistency and availability of the data, the paper has several limitations, especially in the study of urban ecological security indices system, the index weight, data interpolation, the application of remote sensing images and some function modules of the information system, which will be explored and improved in future researches. |
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