An electrographic sensor for determining planar coordinates with good resolution, e.g., about 0.1 mm, and an overall accuracy of about 0.4 mm. A rectangular single sheet of extremely uniform resistive material has a row of small electrodes arranged along each edge with discrete resistors connected between adjacent electrodes of each row so as to form resistor networks along each edge of the resistive sheet. A switching circuit applies a voltage across the resistive sheet by applying one polarity to both ends of the resistor network of one edge and the opposite polarity to both ends of the resistor network at an opposite edge. At a desired time interval, voltage is switched to the second set of resistor networks so as to produce orthogonal electric fields in the resistive material during mutually exclusive time intervals. The sensor is contacted with probe at selected points to produce voltage signals which are proportional to the coordinates of any such points. Specific embodiments are described for punched-card reading, the preprogrammed interpretation of graphical data, and the movement of a probe across the sensor to produce continuous contacting for many applications.