Because of the complexity on the process of map compilation, although there are many kinds of CAD software presently, there is still not a full-automatic map compilation system. It's main reason is that it's not easy to get the generalization mode for varied features on the map, plus the complicated relation among the features that cause many difficulties for map generalization. Therefore, the present research object almost focuses on the generalization of single feature, as to the whole operation of map generalization, only could use interactive approach as the current skill. Upon this point of view this text is according to the writer's research on the drainage basin of near 50 rivers in Taiwan area to establish a set of map river network generalization mode which is suitable that area. In order to concrete the application of automatic cartography, use the River Networks Generalziation System (RNGS), which is researched and developed individually, through the acquisition and processing of information to the graphic output to accomplish the first generalization system in Taiwan which could manage the river automatic selection.