This digital geospatial file consists of a series of raster digital orthophoto images covering all of Cook, DuPage, Grundy, Kane, Kendall, Lake, McHenry, and Will County, Illinois.

The images have a pixel resolution of 0.5 feet which generated an orthophotographic database with a mapping scale of 1" = 100'. The imagery for the "Countywide Flight" was collected between April 2, 2013 and May 7, 2013.

The imagery for the "Special Consideration Area" was collected between April 3, 2013 and June 14, 2013. (Refer to the relevant Process Step for a description of the principal differences between these two flights.)

A digital orthoimage is a raster image of remotely sensed data that has had displacement in the image introduced by sensor orientation and terrain relief removed. Digital orthoimages combine the image characteristics of photography with the geometric qualities of maps. The normal orientation of this data is by lines (rows) and samples (columns). Each sample in this data set contains a series of pixels ordered from west to east with the order of the lines from north to south.

The data set is tiled for dissemination into 18,905 separate tiles, each of which is 2500 feet on a side.

This digital geospatial file has been orthorectified using survey control points obtained through both Airborne Global Positioning Systems and Ground Control Survey. This dataset is projected using the Transverse Mercator map projection. The grid coordinate system used is the Illinois State Plane Coordinate System, East Zone (Zone Number Zone 3776, FIPS 1201), NAD 83 (NSRS2007) (horizontal datum), with ground coordinates expressed in U.S. Survey Feet.

Each tile consists of two files, a TIFF (Tagged Image File Format) (.tif), and an ASCII geo-referencing header file (.tfw). Each tile is approximately 100MB in size resulting in a total of 1.9TB for the region.