AbstractThe studies on automatic extraction of contour lines have attracted interest in building a map information system as an automatic composition of input data. However, many attempts reported so far considered only the local connection relationship of contour lines and did not use global information contained in the whole topographic map. Therefore, they could not cope with extraction of contour lines having various cut forms.The method proposed in this paper can deal with the interconnection of contour lines which are disconnected within a region enclosed by a curved contour line and also the interconnection of contour lines disconnected in the same region, which were difficult in the existing methods. This was because its processing is based on global information of contour lines contained in a topographic map.As an example of the global information, the neighbor relationship built by a Voronoi diagram is used. The proposed method is divided into the following five steps: construction of a Voronoi diagram; identification of neighbor relationships of line segments; determination of height relation of line segments; extraction of contour lines; and extraction of pairs of endpoints to be interconnected. Then, while comparing and verifying them with the features of contour lines, disconnected contour lines are identified and extracted. This paper reports the procedures for processing and then considers the effect of the proposed method by experimental results.