近年來數值高程模型（DEM）的發展不但沒有排除等高線圖的價值，由DEM自動化產生等高線，反而使等高線圖的繪製更為簡便、使用更為普及。然而，DEM的品質問題往往使自動化產生的等高線，存有許多不合理的鋸齒狀型態，包括：水平波紋、邊界不整合及不規則扭曲等三種。本研究採用等高線密度法，有效檢測不合理等高線之分佈，並透過DEM資料的平滑化處理，消除水平波紋的等高線品質問題。

Although Digital Elevation Model (DEM) has become major data for the analysis and display of terrain, however, contour maps are still indispensable for several reasons. Traditional contour maps are drawn manually. Recent popularity of GIS makes the production of contours from DEM much more efficient. During an experiment, we found that the contour lines automatically generated from 40meters DTM of Taiwan demonstrated unreasonable zigzag patterns, including horizontal ripples, marginal discontinuity and irregular warping. These problematic patterns were resulted from the problematic quality of DEM. In this research, we detect these unreasonable patterns by density of contour lines and attempts to improve the quality of the automatic generation. We find that horizontal ripple patterns could be eliminated by smoothing DEM data.