Illinois Digital Orthophoto Quadrangles (DOQs) Illinois State Library
The Illinois State Library has purchased all Illinois Digital Orthophoto Quadrangles (DOQs) that the U.S. Geological Survey produced on CD-ROM for 1988, 1993, and 1998. The DOQ's are in GeoTIFF format. No viewing software is included on the CD-ROMs. The dlgv32 viewing software can be downloaded from the USGS website.
The DOQs on CD-ROM are based on three NAPP (National Aerial Photography Program) flights in Illinois: 1988, 1993, and 1998. The 1988 and 1993 flights were not completely converted to DOQs so coverage is only select. The 1998 flight is completely converted so statewide coverage was achieved. The DOQs are arranged on the CD-ROMs by file number, not alphabetically by quad name, nor by the 5-digit block number from the topographic map index.
The DOQs are arranged on the CD-ROMs by file number, not alphabetically by quad name, nor by the 5-digit block number from the topographic map index. To find a DOQ for a specific quarter quad, State Library staff created this alphabetical index, translating the quad name to CD-ROM file. The left hand column is the name of the quad. The next column to the right is the quarter quad, i.e., NE, NW, SE, or SW. The third column to the right "flight date" is the date of the aerial photography on which the DOQ is based. Some quads have more than one flight, but they are integrated by the quad name. The fourth column to the right is the "series" and "file" numbers.
Because the State Library purchased these DOQ's in several different orders, USGS numbered the "files" beginning with one for each order. Therefore, a "series" was necessary as well. The fifth, and last, column to the right "data file" is the 5-digit block number, plus a 1, 2, 3, or 4 for the specific quarter: 1= NW, 2 = NE, 3= SE, and 4 = SW. You need a series and file number to get to the right CD-ROM and the 5-digit block number to get to the right data on the CD-ROM. The call number for these CD-ROMs is: SOFTWARE I 19.124/13: Ser. [no.]/File [no.]
Note: The State Library owns the 2005 statewide digital orthoimagery as well. For more information, or for a print version of the index to the DOQs on CD-ROM, please call 217-782-7596 or email firstname.lastname@example.org.