Abstract: The line-data generating unit of this apparatus automatically reads a map image through an image scanner, generates a digital-image signal in a pattern-recognition module, prepares line data in a line-data image processing unit, and stores the line data in RAM (I). A data converter retrieves the line data from the line-data generating unit, prepares plane data, and issues the plane data to a property-data preparation unit. Through a closed-area-data image processing unit, the property-information preparation unit, based on instructions input from a keyboard, interpolates points of discontinuity in the plane data; assigns properties corresponding to such points, and prints the output. RAM (II) stores completed data. The interpolation of points of discontinuity in the plane data is performed jointly and simultaneously by input terminals PCi (i=1, 2, . . . , n).