Study on the Algorithm of Contour Curvature in Topographic Map

Contour curvature is one of the fundamental topographic indices in digital terrain analysis.Calculating contour curvature on contour lines directly is of great significance to quantitative analysis of contour complexity and definition of reasonable DEM resolutions.This paper developed an algorithm named circle fitting to calculate contour curvature using single contour according to the mathematic sense of curvature.Contour curvature is calculated and analyzed in loess hilly region,loess tableland region and undulated hilly region in northeast China.Preliminary results are as follows:(i)contour curvature is greater where contour line is more curved or where terrain is more complex,and smaller where contours are straighter or the landform is simpler,the range of contour curvature is 0.000/m to 1.564/m;(ii)the mean value of contour curvature increase from undulated hilly(0.025/m)in northeast,loess tableland sample region to loess hilly sample region(0.086/m);(iii)the spatial distribution of contour curvature well corresponds to terrain characteristic.The calculation result is reasonable.Issues to be further studied are also discussed,including the relationship between contour curvature and terrain convexity,relationship between contour curvature and other topographic indices.