By using the impedance perception algorithm, which we previously proposed, the stiffness matrix that constrains the motion-force relation of a robot's end-effector is calculated in real-time. In this paper, we describe methods of extracting information concerning certain local properties of object surfaces from the stiffness matrix when the end-effector is slid on the surfaces. We develop two algorithms to deal with two classes of surfaces: flat and convex cylindrical surfaces. Since the proposed methods are designed separately from control strategies, they can be used for both autonomous and remote controlled robots. The results of preliminary experiments are presented.