Improvement Of Classification Unit Division Method Based On Semantic Rules And Comprehensive Scale Research

Farmland classification and grading began in the late 1980 s,including the grading results and ranking results.The grading results mainly reflected the natural quality of long-term stability of farmland quality difference.Ranking results,refine the difference between the actual quality,primarily reflected the farmland comprehensive quality level,intensive utilization,economic characteristics difference.With the improving of the precision of farmland quality evaluation,the refinement of land use classification,the land parcel can’t meet the need of refining the quality of cultivated land.As the result,the unit must consider multiple factors affecting the quality of cultivated land.Overlay method could comprehensively analysis the various factors,which tends to produce a large number of finely unit,led to the unit too broken.Therefore,it is of great significance to scientifically improve the division method of grading units.Based on the 6 areas as the research area,taken across the Qinghai province latitude of 35 ～ 37,including the eastern loess plateau region,Qilian mountain region and Qaidam basin region.With the 2016 annual cultivated land quality update database as the research object.This article considering the land use,soil characteristics landforms,climate and other factors,formulate the semantic rules,geometric rules,and integrated constraint rules.Through the analysis of Arc GIS mapping synthesis method,using Python as the scripting language,make the automatic grading unit division model,which could solve the problem of comprehensive processing of finely spots.Through this method,grading units could be scientifically delineated.The relatively consistent internal attributes and the external difference are the basic criterion of unit division.Besides,the degree of unit fragmentation is an important reference index to build the evaluation standard of unit division quality.A comprehensive comparison experiment with the minimum unit area of 400m2,800m2,1200m2,1600m2 and 2000m2 was conducted on the overlapping results of each topographic area,focusing on the exploration of the optimal comprehensive scale of cultivated land units in different topographic areas in Qinghai province。The analysis of the evaluation result shows that the improved unit division method can effectively solve the problem of finely unit produced by the superposed method.With the minimum unit of 800m2 as an example,the quantity of the unit can be reduced by 4.0% on average,while the total unit internal variance increased by 0.08%.In eastern loess plateau region,the effect of comprehensive experiment in 800m2 as the smallest is best.In the Qilian mountain region,the effect of comprehensive experiment in 1200m2 as the smallest is best.In Qaidam basin region,the effect of comprehensive experiment in 2000m2 as the smallest is best.The minimum unit area of each experimental area from east to west basically increases with the decrease of the number of cultivated land,which is closely related to the basic situation of cultivated land distribution in each topographic,geomorphic conditions,the degree of fragmentation,and the complexity of soil climate.Generally,the unit comprehensive score of each area increases firstly and then decreases with the increase of the minimum unit area.