Illinois Digital Raster Graphics (DRGs) Illinois State Library
The Illinois State Library purchased the entire state set of Illinois Digital Raster Graphics from the U.S. Geological Survey (USGS) on CD-ROM as of 2001. The 15 CD-ROMs contain all the 1:24,000, 1:100,000, and 1:250,000 topographic quadrangle maps covering Illinois in 1,138 files.
The 1,138 files are in file number order on the 15 CD-ROMs, not alphabetically by the name of the quad or by the 5 digit block number from the topographic map index. State Library staff created these alphabetical indexes, translating the quad name to the file number and 5 digit block number for each of the three scale series. You need the 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 19.128:IL 6/File (nos.).
Please be aware that the digital version is not more recent than the published paper topo quad. In fact, since the State Library is not purchasing the revised Digital Raster Graphics, the Digital Raster Graphic may be older than the latest quad in some instances. For more information, or for a print version of these indexes, please call 217-782-7596 or email email@example.com.