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:
- Band 1 = Red (598-675 nm)
- Band 2 = Green (500-650 nm)
- Band 3 = Blue (400-580 nm)
- Band 4 = Near-IR (675-850 nm)