The U.S. Geological Survey recently undertook the investigation of two seemingly unrelated cartographic tasks: (1) the preparation of map copy for digitizing and (2) the production of experimental slope maps. Both tasks, however, require techniques and equipment for changing or manipulating the line weights of existing map symbols and producing suitable reproduction copy. After a study of existing equipment, a prototype revolving illuminator was designed and fabricated for experiments in line-weight manipulation. Sufficient exposures have been made with the device to indicate that positive control of line-weight increases and decreases up to 0.2 inch is attainable. The device has been used for photomechanical experiments in slope mapping, hill shading, and preparation of map copy for digitizing.