AMS M791 (GSGS series 4229). AMS 3. Copied from an Istituto Geografico Militare map dated 1931 and compiled by the U.S. Army Map Service in 1944. This sheet shows revision to principal communications from smaller scale maps and air photos from 1944. Road classification is NOT based on reconnaissance, reliability is uncertain. The meridians are based on the meridian of Rome, which is 12 degrees, 27 minutes and 7.1 seconds east of Greenwich. Contour interval 50 meters. North Italy Zone Grid.