Illinois Historical Aerial Photography 1938-1941

Statewide aerial photographs were first acquired for Illinois from 1938 through 1941. This collection history gives details about the more than 30,000 photographic paper prints. The original silver nitrate film negatives were destroyed by the National Archives in the 1980s due to deterioration and instability. 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.

ILHAP File Availability

Data Distribution: Compressed Data

Digital files are offered as LizardTech's MrSID .sid files, in either first generation or Generation 2 .sid file formats. Target compression ratios were 12:1 or 6:1, respectively; one compressed file is roughly 3 megabytes or 7.5 megabytes in size, respectively.

Digitization, or print scanning, has been completed for 62 counties in Illinois (shown in dark green) in an effort to create a lasting archive of this irreplaceable collection. The aerial photographs have not been georeferenced. Adjacent aerial photographs can be used for stereoscopic viewing.

Illinois Historical Aerial Photographs are available free-of-charge via:

a list of counties (62 counties) for data viewing or download, or

an interactive map (58 counties) for data viewing or download.
    How to use the Map.

Metadata:

ilhapmeta.zip contains the following:

• ilhap_gen, overall metadata for the county aerial photograph collections.
• ilhap_nav, generic metadata for the county index data layers.
• l_index, metadata for the schematic (line) indexes.
• p_index, metadata for the photo mosaic indexes.

Metadata standards: FGDC, Dublin Core, and MARC.

File indexes:

Index data shapefiles and photograph and/or line index images are available for each county.

Resources:

ExpressView Browser Plugin from LizardTech allows you to view .sid files.

File Distribution: Uncompressed Files

Contact the Illinois State Library to obtain indiviual, uncompressed Illinois Historic Aerial Photograph files.

Data Acquisition

Historically, photographs were taken in discreet collections by county. Labels were stamped on each aerial photograph; the 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 Support for Data Distribution

Project funding was contributed by: Champaign County Regional Planning Commission, Illinois Department of Natural Resources (IDNR), Illinois Department of Transportation, IDNR Office of Resource Conservation, Illinois State Geological Survey, Illinois State Library, Illinois Waste Magagement Research Center, Institute of Museum and Library Services, Jo Daviess County Soil and Water Conservation District, Lake County, Illinois, US Army Corps of Engineers, and Winnebago County GIS.