Abstract: An electrographic sensor for determining planar coordinates is described whereby graphical material to be analyzed may be placed beneath, or projected against, the rear surface of the sensor. This sensor is of particular value for placing on the face of a cathode ray tube. The sensor includes a rigid, optically transparent substrate having an extremely uniform, substantially transparent resistive layer applied to one surface, small electrodes in contact with the resistive layer and individual resistors connected between adjacent electrodes to produce a resistance network around the perimeter of the substrate. Means are provided to produce orthogonal electrical fields in the resistive layer whereby the contacting of the resistive layer with a conductive stylus produces voltage signals at the stylus which are proportional to the coordinates of the point of contact. The second surface of the substrate may be made translucent for projecting optical images thereagainst.