Abstract: This paper presents a new measurement of image matching. The measurement takes account of accumulation of discrepancy signals, distribution of discrepancy signals, and treatment of preternatural discrepancy signals. Based on the measurement, this paper presents, at the same time, a new algorithm for extracting features with symmetric figure on scanned topographic map. Effectiveness and practicability of the new measurement and the new algorithm are explained by some actual examples. It is important for vectoring of scanned topographic map and theory of pattern recognition.