Errors of slope and aspect estimated from digital elevation models derived from1:25,000-scale topographic maps

Abstract

We examined the errors of slope and aspect calculated from digital elevation models (DEMs) derived from １:25,000-scale topographic maps published by the Geospatial Information Authority of Japan (GSI). First, we generated DEMs with spatial resolutions of１０mfromcontoursat 10-m intervals and spot elevations in “Fundamental geospatial data (level 25000)”generated by GSI and a DEM with a spatial resolution of 10m from 10-m mesh data, the “Fundamental geospatial data (grid altitude information)”generated by GSI. We calculated the slope and aspect angles from the DEMs. Then we established 10×10-m experimental plots corresponding to DEM cells in forests using the global positioning system and a laser range finder, and measured slope and aspect angles with a clinometer at the centres of the plots. Finally, we determined errors in the estimates from the DEMs using the plot measurements. The estimates of slope were not biased, and their root mean square errors (RMSEs) were less than 10 degrees. Excluding sites with gentle slopes, the estimates of aspect were not biased, and their RMSEs were less than40 degrees. However, we note that the estimates of aspect could have large errors at sites with marked changes in slope or aspect such as valley lines and ridge lines, despite wider horizontal contour distance.