Illinois State Library

Digital Orthophoto Quadrangles (DOQs)

The Illinois State Library has purchased all Illinois Digital Orthophoto Quadrangles (DOQs) that the U.S. Geological Survey has produced on CD-ROM. The DOQ's are in GeoTIFF format. Information about DOQ's and GeoTIFF can be found at http://mcmcweb.er.usgs.gov/sdts/geotiff.htm. No viewing software is included on the CD-ROMs. The dlgv32 viewer, for DOQ's and other USGS products, can be downloaded from http://tahoe.usgs.gov/viewers.html.

The DOQs are based on all 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 has been achieved. The DOQs are in order 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, Illinois State Library staff has created an alphabetical finding guide, 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 Illinois 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.]

Index to Digital Orthophoto Quadrangles (DOQs) at the Illinois State Library PDF

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