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2011 Illinois Department of Transportation Orthophotography

2011 Acquisition by Month

Map of 2011 IDOT Orthophotos by month of image capture.

The Illinois Department of Transportation (IDOT) coordinated the funding and acquisition of the 2011 digital orhtophotography for 95 counties in Illinois. The metropolitan Chicago area including Cook, DuPage, Kane, Kendall, Lake, McHenry and Will counties were not acquired as part of this IDOT project. The native projection for the 2011 IDOT orthophotography is transverse Mercator, Illinois State Plane Coordinate System (SPCS), West and East zones, NAD 1983 datum.

For the purposes of data delivery and distribution, the orthophotography is organized into data tiles, each covering a geographic area of 10,000 ft. x 10,000 ft. The ground spatial resolution of each orthophoto tile is 1 ft. x 1 ft. per pixel for 93 of the 95 Illinois counties. Because of a county cost-sharing option made available as part of the 2011 IDOT orthophotography project, higher resolution orthophotography with a ground spatial resolution 0.5 ft. x 0.5 ft. was processed and is available for Sangamon and Tazewell Counties, as well as a portion of Woodford County. Each data tile was created utilizing multiple aerial images. The metadata for each tile will show the date the imagery was captured.

Images were captured between March 16th and May 30th, 2011, using a Z/I Imaging Digital Mapping Camera (DMC). The DMC system collects imagery in four spectral bands, and therefore users can select between either a natural color rendition (RGB = 1,2,3) or near-infrared rendition (RGB = 4,1,2) for a particular application:

Data Distribution: Uncompressed Data

Full Resolution data will be available for download as a Zip file bundle. Each Zip file will include a GeoTIFF (tif) file, a georeferencing world file (tfw), and metadata (xml). Average file size of each GeoTIFF file is 381 MB before Zip bundling. Lossless compression was used in the Zip bundling of these files and the final Zip files will vary in size.

A statewide collection, excluding the 7 Chicago Metropolitan Area counties, of full resolution data requires about 7.3 Terabytes of storage space.

    Available here soon!

Data Distribution: Compressed Data

Compressed data are available via a Zip file bundle. Each Zip includes a compressed image (Jpeg 2000) and a metadata file (xml). Jpeg 2000 (jp2) files were created from the full resolution GeoTIFFs using LizardTech's GeoExpress 7. Target compression ratio was 15:1; one compressed file is roughly 25 megabytes in size. No added compression (including lossless compression) was used in the zip bundling of these files.

A statewide collection, excluding the 7 Chicago Metropolitan Area counties, of compressed data requires 500 Gigabytes of storage space.

IDOT 2011 compressed data are now available free-of-charge via:
Countywide Collections - 63 SPCS East zone County Zip files & 68 SPCS West zone county Zip files new
    note - 34 counties overlap the SPCS East/West zone boundary
Available Soon- an interactive map for data download and viewing of individual tiles [6,695 tiles in SPCS East zone & 10,381 tiles in SPCS West zone]

    Compressed Zip file bundles for individual tiles contain:
<filename>.jp2 - compressed JPEG 2000
<filename>.xml - metadata file for uncompressed GeoTIFF image, edited to include compressed image information

IDOT 2011 Collection metadata available soon.

File indexes:
IDOT 2011 Tile Indexes - Esri shapefile format tile indexes, county and statewide - SPCS East and West zones

State Plane Coordinate System file naming convention based on data tile coordinates.

Project Support for Data Distribution

Project funding was contributed by funds from Illinois Department of Transportation via the Illinois Height Modernization Program.