Digital Elevation Model (DEM) is indispensable for much analysis such as topographic feature extraction, runoff analysis, slope stability analysis, landscape analysis and so on. Such analysis requires a high accurate DEM. The accuracy of DEM is usually represented by spatial resolution and height accuracy. Slope is one of the crucial terrain
variables in spatial analysis and land use planning, especially in the mountain region which is suffering from serious soil
erosion. However slope accuracy derived from DEM usually does not match with its popularity. A quantitative simulation to slope uncertainty is important not only theoretically but also necessarily to applications. The objective of this study was to analyze the slope uncertainty of Yizi following GIS based on different DEM resolution. Comparative and math-simulation methodology was employed for data processing and analysis. There is a linear correlativity between
mean slope, slope change rate and different DEM resolution within the study area, and the analysis and simulation result shows that different DEM resolution has great influence on slope uncertainty. This methodology applied in this study should be helpful to similar researches in spatial data uncertainty investigation.
A study on the change feature of the construction land is very important to the construction land plan and management in
Sichuan Province. Therefore, this paper tries to discover the change feature of the construction land in Sichuan province
by using the technologies of remote sensing and GIS. The dynamic change feature revealed in the paper is that the net
increased construction land totally amounts to 33854 hectares that is mainly resulted from the transformation of
cultivation, accounting for percent 84. In terms of the environment features of the construction land change, the net
increased construction land that mainly occurred in the regions with the slope below five degree accounts for percent 88
while that mainly occurred in the regions with slight and light soil erosion accounts for percent 94 and that mainly
occurred in the regions with the environment quality grade above grade seven accounts for percent 91. The spatial
distribution feature of the construction land change is that the net increased construction land is mainly distributed in the
plain and hills, accounting for percent 80, and mainly distributed in Chengdu, Leshan, Meishan and Mianyan cities,
accounting for percent 53. It was also shown that the cites whose construction land sprawled above 0.7 times their areas
in 1995 included Ya'an, Zigong, Leshan and Mianyang.
The tropical forest change of Xishaungbanna in P.R.of China was studied here, which includes several steps. Firstly, The LANDSAT TM images acquired respectively on March 26, 1987, February 10, 1997, and March 6, 2000 were geometrically corrected, matched, and radiantly corrected. Secondly, the Normal Different Vegetation Index (NDVI) was formulated for the three periods. Thirdly, the false color composition images were achieved respectively for the three periods, which were used for visually interpreting forest and non-forest. Fourthly, the forest areas of the three periods were extracted semi-automatically from NDVI of the three periods by their suitable threshold. Fifthly, the forest areas of the three periods were changed into vector form. Sixthly, the extracted forest area of the three periods in vector form superposes their false color composition images for evaluating their accuracies. Finally, the map of forest change among the three periods was made, and the forest change area was calculated. The research shows: The decreased tropical forest area between 1987 and 1997 is 234558 hectares, accounted for 19 percent of the tropical forest area in 1987. The decreased tropical forest area between 1997 and 2000 is 41237 hectares, accounted for 4.2 percent of the tropical forest area in 1997
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