Abstract: On the basis of the feature of spatial information of map and the particularity of its decision table when apply rough set theory and method to map generalization, an idea of discretize the continuous conditional attributes in the decision table by the method of discretizaton with nonsupervision before adding decision attribute according to the vague categories of spatial objects which obtained by the application purpose of decision table is proposed. Then calculate the importance of the conditional attributes by the method of attribute reduction of rough set to access the importance degree of spatial objects with dynamic sequencing. This process can resolve the problem of can not determine the decision attribute inadvance when apply rough set theory to map generalization, and the experiment result of spatial points selection shows its rationality and validity.