Abstract: On assessing the quality of a map, in case no large scale map for comparison isavailable, fraditionally indirect inference is made with the help of the map projections,nomalization degree of map symbols, the time when it is mapped and mapping organi-zations, but the inference is not always reliable. This paper suggests that the inferencebe made using mathematical model of map feature's distribution. Taking rivers for exa-mple, this method and mathematical model used in the inference are discussed. Finallypractical examples are given to prove that this kind of inferring method is reliable.