The requirements for the simplification of contours are explained, and existing approaches for the generalization (i.e., simplification and smoothing) of contours are briefly summarized. Skeleton lines (i.e., drainage and ridge lines) are supposed to provide information for the determination of characteristic parts of contours. Characteristic points are automatically determined during the process of deriving skeleton lines from contours in accordance with the method developed by Aumann, Ebner, and Tang (1991). Three widely used algorithms for the simplification of contours - nth point, distance tolerance, and Douglas-Peucker - are examined. They are analysed with respect to the retention of characteristic parts of contours, based on case studies. Finally, the algorithms are modified in such a way as to consider the determined characteristic points. A new simplification criterion is included in the algorithms, ensuring that they retain the characteristic parts of contours.