Statewide aerial photographs were first acquired for Illinois from 1937 through 1947. This collection history gives details about the approximately 33,500 photographic paper prints that were scanned. The original silver nitrate film negatives were purposefully destroyed by the National Archives in the early 1980s due to deterioration and instability. An attempt to copy the negatives prior to their desctruction resulted in a very poor quality replacement. Due to this fact the original photographic prints are now the best substitute for the negatives. Use of the paper prints over time has resulted in their becoming faded, worn, defaced, or lost. Access to these print collections is becoming increasingly restricted.
Digitization, or print scanning, has been completed for statewide coverage of Illinois in an effort to create a lasting archive of this irreplaceable collection. The individual aerial photographs distributed here have not been georeferenced. Adjacent aerial photographs can be used for stereoscopic viewing in most areas of the state (except portions of Carroll, Piatt and Stephenson Counties).
JPEG File Format
This format is a compressed file with the following file extension
.jpg. The original TIFF format files were compressed using Adobe
Photoshop CS4 and their Quality setting was set to 10. The average file size is approximately 7.25 megabytes for 7x9 inch photos and 9.25
megabytes for 9x9 inch photos. These files should open in most browsers as they are an open source file format. These files have not been georeferneced.
MrSID File Format
This format is a compressed digital file with the following file extension
.sid. The original TIFF format files were compressed
using LizardTech's GeoExpress software in Generation 2 .sid file format at a target compression ratio of 6:1. The resulting average file
size is 5.5 megabytes for 7x9 inch photos and 7.5 megabytes for 9x9 inch photos. These files require a special viewer (ExpressView browser
plug-in, available below) in order to view them online. They will also open in some mapping software (despite not being georeferenced) once
they have been downloaded. The ExpressView browser plug-in is not available for Macintosh OS X or higher and is getting increasingly difficult
to find for Mac OS versions earlier than OS X. These files have not been georeferneced.
TIFF File Format
This format is a full resolution file format with the following file extension
.tif. These are the original uncompresed files.
They were scanned at 750dpi on a Crosfield Drum scanner. The average file size is approximately 36.5 megabytes for 7x9 inch photos and 47.5
megabytes for 9x9 inch photos. These files require a browser plugin to be viewed online. Many
software programs will be able to view the images once they are downloaded. These files have not been georeferneced.
Please read the license agreement. This link also provides citation information.
Historically, photographs were taken in discreet collections by county. Labels were stamped on each aerial photograph; the annotation information contained film roll number and exposure number. Naming conventions for the digital files include codes for county, film roll number, and exposure number; zeros are used as placeholders. Flight line information is not included in the digital file-naming conventions or the original stamped labels.
|Example: The file named 0bwq04063.sid is labeled 4-63 on the photograph.|
|County Code:||0bwq||BWQ = Cook County|
|Roll Number:||04||Roll 4 of Cook County|
|Exposure Number:||063||Exposure 63 of Roll 4|
Project funding was contributed by:, , , , , , , , Jo Daviess County Soil and Water Conservation District, , , and .