Evaluation method of historical economic value of cultivated land in data-lacking regions of Tibet based on GIS

Data-lacking regions have little information about the economic value of the cultivated land in the historical years. This research chose Lhasa city in Tibet as an example to discuss a method based on GIS (geographic information system), which was to propose the historical economic value evaluation of cultivated land in data-lacking regions and to fill the blanks of the historical economic value data of the cultivated land. This research took 3 factors based on the agricultural location theory from natural and human aspects, i.e., the slope, the stable light at nighttime, and the distance from the cultivated land to the roads at different levels. The data resources of this research were defense meteorological satellite program/ operational linescan system (DMSP/OLS), digital elevation model and the road data, all of which were free and easy to acquire. In addition, all of the data were in the year of 2010 in order to ensure the data quality and have the corresponding Google Earth data which were treated as the ground true reference. First of all, we graded each factor into 5 classes and assigned them the score of 1, 3, 5, 7 and 9, which indicated their contributions for improving the economic value for the corresponding cultivated land. Second, we decided the weights for each factor in each grade by employing the method of analytic hierarchy process. Third, the spatial weighted overlay based on GIS was introduced to calculate the final score for each cultivated land which was the reference to determine their historical economic value. The method was firstly testified in the Chengguan district, Lhasa city and then applied to the whole city. We classified the cultivated land in Chengguan district into 3 classes, and the first class cultivated land referred to the farmland which had the highest historical economic value and the third class referred to the lowest one. After that we introduced the stratified random sampling method into this research to perform the accuracy assessment. We selected 100 pieces of cultivated land according to their area and compared the evaluation result with the ground true data by visual interpretation. The overall accuracy of the historical economic value evaluation of Chengguan district was 84% which meant that the proposed method was very effective. Instead of applying the method to the whole city directly, we took the economic differences among the 8 counties into account. We classified the economic level of the 8 counties into 3 class based on their stable light intensity with the help of the nighttime light satellite imagery before the method was extended to the whole Lhasa city. The accuracy assessment was also performed by the randomly selected 1000 pieces of the cultivated land in the whole city. The overall accuracy of the evaluation was 82.6% with an overall Kappa coefficient of 0.722, the user??s accuracy of the first-class cultivated land was 79.63%, and the producer??s accuracy was 71.27%; the user??s accuracy of the second-class cultivated land was 84.76%, and the producer??s accuracy was 80.91%; the user??s accuracy of the third-class cultivated land was 81.58%, and the producer??s accuracy was 89.97%. The result indicated that the extended method based on the nighttime imagery was scientific and effective to apply the evaluation method proposed in this study to a larger study area, and this method was robust and easy to realize. In summary, the area of the cultivated land in middle level accounted for 58.43% of the total area. Chengguan district, as the center of Lhasa city, had the most highest cultivated land value, and the Linzhou county had the lowest economic value of cultivated land. Further work should focus on the realization of this method in other years, which helps discuss the change trajectory of the cultivated land economic value in time series.