The Study On The Spatial Decision Of The Reclamation Of Agrarian Land For Afforestation Based On Geographical Information System

the project of land conversion from farmland to forest or grassland is a system engineering, whose span of time, scale and field must be long, broad and wide-ranging. Based on this reason, it has not merely affected the first-hand benefit of millions upon millions peasantries, and also affected the problems of cereals food security and water resources equilibrium moreover. The predominant Problems existing in the process of the project implementation rest with how to ensure the key theories and technique methods in harmony with a series of conditions, such as the level of social-economic development, the needs of ecological environment construction and protection, the cereals food security and the ecological utilization of water in a specially designated region. The aspects relating to these correlations theories and technique methods include "choice of de-farming lands", "the number of de-farming lands", "selection of plants planted in the de-farming lands", "the research for patterns of vegetation rehabilitation on the de-farming lands" and so on. Hence, Under the guide of ecological rehabilitation theory and sustainable development theory and with the software platform of geographical information system and the corresponding methods of mathematical analysis, the article takes Zhangbei county of Hebei province, situated at the ecotone of Bashang altiplano, as the object of study and the effective ways and methods aimed to resolve to the above problems are probed.the conclusion of the study indicated that it is the basis to develop effectively the decision-making research for the project of land conversion from farmland to forestland that the synthetical applications of geographical information system and the database technique to build the background database of the project of conversion from farmland to forestland. With GIS software of MapInfo and ERDAS and database software of FoxPro, etc, the map of plot and maps of key elements are created through a series of operation such as graph data inputting by scanner, screen digitizing, overlapping, etc. Through a series of processing such as attribute data inputting, digital coding, programming and so on, the attribute database is created. Through setting up key field, the mutual querybetween each other has been realized. Finally, the fundamental information database for reducing cultivated land to plant forest and grass in Zhangbei county has been established.Based on the diagnosis of the present situation for land resources, simultaneously, using principle components analysis and Delphi method, this paper sets up an index system of land assessment. The weight of each indicator is calculated by using the method of Analytic Hierarchy Process (AHP) and Delphi method. In the process of the land synthetic assessment, the plot was taken as evaluating unit, complex-index method and limited-factor method are combined to use on assessing land resources. The critical values of assessment classification and the calculating method were given in the paper, comparing with the actual data that the result was satisfied. Theoretically, the result resolves the problem of how to ensure the directions for land utilization, that is, the problem of "where ought to retreat".Using Maplnfo, critical suitable and unsuitable farmland must be chosen to replace by forest or grassland through overlaying analysis of land-use map and suitability evaluation map. Finally, the de-farming plots and plots of replacing farmland by forest or grassland have been ensured using the SQL model. Based on the study, some results are shown as the follows: the first, the total area of the de-farming land is 51 277.2 hectare, 40.1 percent of total area of cultivated land. The second, the area of cultivated land returning forest is 13 245.9 hectare, 25,8 percent of area of de-farming land. The third, the area of cultivated land returning grass is 38 031.3 hectare, 74.2 percent of area of de-farming land. Theoretically and technically, the result resolves the problem of "the number of de-farming land".Bas...