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There are so many mountains in South Korea and different mountain systems can be found in diverse scale.In general,drainage basin has been used as the unit of a regional classification.And mountains have been considered as the boundary of that region or as one of the geological items based on the mountain systems.As shown in defining the boundaries of national reserves,national parks,provincial parks etc.,however,the mountains have been used as the unit of their classification.Therefore,it is considered that mountains can be also used as the unit of ecological or geographical analysis.This study classified South Koreas mountains based on the mountain ordering using 1:250,000 digital topographic maps and analyzed the relationships between mountain orders and geomorphometric variables such as mountain number,relative altitude,relief,slope,roundness of boundary,etc.Mountain order was defined in terms of closed contour lines(100m interval) on the digital topographic maps.A set of closed,concentric contour lines defines a first-order mountain and that have only one closed contour line for each elevation.Because the boundaries of classified mountains are defined on the contour lines,the classified lines are very distinct and the classification system is possible to apply to the any kinds of topographic maps with contour lines.The idea of mountain ordering has been derived from the stream ordering of Strahler by Yamada Shuji(1999).In order to conform the suitability of 1:250,000 digital map for this kind analysis,a pilot test was conducted for two small islands(Namhae: 301 ?,Geoje: 378 ?).The ratio between mountain orders and mountain number from 1:250,000 maps was so similar to that from 1:25,000 digital maps.Fifth-order mountains are the highest order mountains in South Korea,which include Youngnam Alps,Jiri-Deukyu Mountains,and Taebaek-Seulak Mountains.10 independent forth-order mountains which are not included in fifth-order mountains are identified and 80 independent third-order mountain are also identified.7 of 16 national parks excluding 4 coast-type National Parks in South Korea are included in the boundaries of fifth-order mountains and the remains are included in those of forth- and third-order mountains.Although more detail DEM based on the larger scale digital maps could be constructed,the contour lines of 1:250,000 digital maps were not identical to those from other DEMs.Therefore,DEM(100 X 100m) of 3 fifth-order mountains was constructed from 1:250,000 digital maps using ARC/GIS module and the value of geomorphometric variable for the ordered mountains were obtained from the analysis of that DEM.Some meaningful normal-log relationship between mountain order and mountain number,relative altitude,relief,and roundness can be obtained.The result from the average slope analysis shows a different pattern from those results above.The average slope of first-order mountains was lower than those of second and third order mountains.It may be considered that the lower slope in first-order mountains was due to the presence of high-level planation surfaces on the crests of fifth order mountains.Not being tried in this study,the analysis of relationships among the geomorphometric variable will be contributed to the understanding of the relief structure of ordered mountains in South Korea.