Flights flown between August 7, 1938 and September 4, 1939 by Iowa Aerial Surveys, Inc., for the U. S. Dept. of Agriculture, Agricultural Adjustment Administration. Photos numbered BGS-1-4 through BGS BGZ-2-100. Scale not given. Stereoscopic coverage. Only indexes are georeferenced.
Johnson County (Ill.) (W 89°03′--W 88°42′/N 37°36′--N 37°18′)
Illinois State Geological Survey
219 remote-sensing images, 860 megabytes, average file 3.9 megabytes
Scanned from 9 x 9 contact prints (nominal scale ca. 1:20,000) on Crosfield 646IE drum scanning system at 750 dpi. Quality assurance target not published but available by contacting the Illinois State Library Map Dept. MrSID files compressed at a target ratio of 12:1. Uncompressed TIFF images on cd available from the Illinois State Library Map Dept.