We present a filter to detect the edge of potential-field image. The filter is computed in the space domain using a simple nine-point convolution filter basing on the ratio the total horizontal gradient and the total gradient. The filter is to apply edge-detection as a useful tool for potential field interpretation on synthetic data. Finally, the proposed filter is applied to a field example from the Finger Lakes region of State of New York, where the results are in good agreement with previous results and present new structural features.