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Topological consistency which plays an important role in land-use map is a difficult problem for map auto generalization. This paper concentrates on the topological preserving of river's dimension-reducing generalization in the land-use map. We propose a method for handling the conflicting constraints involved in generalizing a river polygon (double-line river) into a single-line river. It includes mainly two steps: First, extract the medial axis as a centerline for river polygon base on the constrained delaunay triangulation model. Then, expand the polygons' boundaries which are shared by the double-line river's bank towards the collapsed river's centerlines base on the topology and computational geometry. Experiments are tested against land-use maps at 1:10k scale. The results illustrate that this method can keep the topological constraint well for river dimension-reducing generalization in land-use map.