Kang-Tsung Chang

The Effect of DEM Resolution on Slope and Aspect Mapping

This article examines the effect of the spatial resolution of digital elevation models (DEMs) on slope and aspect data. After a review of computing methods for slope and aspect and such factors as DEM resolution, topographic complexity, and quality of DEM data, the article presents two experiments using DEMs from 8 to 80 m intervals. Results of the experiments show that the accuracy of slope and aspect data, as well as the mean and standard deviation of slope values, decrease with lower DEM resolutions. Comparison of slope and aspect maps generated from different resolutions reveals that slope differences concentrate in areas of steep slopes, whereas aspect differences are in generally flat areas with minor landform features. Slope differences can be explained statistically by relative relief, and aspect differences by relative relief and standard deviation of elevation.

Analyzing Spatial and Temporal Changes of Aquaculture in Yunlin County, Taiwan∗

Abstract This article analyzes spatial and temporal changes of aquaculture land use in Yunlin County, Taiwan, and discusses the driving forces for these changes. Digital land-use maps and satellite imagery for 1982, 1988, 1994, and 2002 were used to extract aquaculture areas. A geographic information system was used to derive changes in aquaculture areas and to compute the spatial clustering statistics over time. A survey of eighty-seven farmers was conducted to obtain their views and concerns about aquaculture. The results show a rapid expansion in aquaculture during the 1980s, driven mainly by exports to Japan, and a continuous decline since the mid-1990s because of economic, environmental, and demographic factors.