Service robots are being developed as a supportive aid for elderly people. Those robots are operated by non-expert users in heterogeneous domestic environments. Hence, the ability of a robot to be operated in a more natural human friendly manner enhances the overall satisfaction of the user. Humans prefer to use voice in order to convey instructions. Those voice instructions often include uncertain terms such as “little” and “far”. Therefore, the robotic assistants should possess the competency to appropriately interpret the quantitative meanings of such terms. The quantitative meaning of uncertain terms related to the spatial information depends on the spatial arrangement of the environment. This paper proposes a method in order to evaluate the uncertain information in user commands by replicating the natural tendencies of humans about the spatial arrangement of the environment. A module called Occupied Density analyzer has been deployed to analyze the occupied density distribution. A function has been defined to estimate the perceptive distance based on the occupied density distribution. The perception of the uncertain terms is adjusted according to the perceptive distance of that particular scenario. Particulars on rationale behind the proposed method are explained with due attention to the natural human tendencies. Experiments have been carried out in order to evaluate the performance and the behaviors of the proposed system.