It is important to set landmarks when a robot needs to navigate in a certain environment and to measure its own location; however, it has not been discussed well how to arrange landmarks in the optimal way until now. We, therefore, demonstrate the possibility of design of the optimal arrangement of artificial landmarks. First, we make it clear the optimization problem with regard to the arrangement of landmarks. Second, as one example of the artificial landmarks, we introduce a signboard system. Third, we propose a methodology to evaluate arrangement of landmarks assuming an obstacled rectangular environment. Fourth, we apply the algorithm of spatial competition to the optimal arrangement of landmarks. Finally, simulation results indicate that even though our method is not global optimization approach we can obtain closely optimal and practical arrangement with the minimum number of landmarks which satisfies the necessary condition.