This article compares Dempster Shafer's evidence methods' and fuzzy union operators' accuracy and speed criteria for real-time map building process. For real-time applications, it's very important to choose the right operator which can give good results rapidly for different kind of environments. In this study, several fuzzy union techniques are used to integrate sonar measurements for the map representation. The advantage of the method over Dampster-Sheafer approach is discussed. Experimental studies are taken on Nomad 200 Robots simulation environment.