2005 Illinois Chicago Urban Area Orthophotography

Chicago Urban Area (CUA) orthoimagery data have been created for the counties of Cook, DuPage, Kane, Lake, McHenry, and Will in northeastern Illinois in two projections. These are Universal Transverse Mercator (UTM) with a NAD83 datum, Zone 16 and Illinois State Plane East Zone (SPE) with a NAD83 datum. Data were created using US Geological Survey Urban Area specifications on true-color film during the leaf-off period of spring, 2005 at a 1 foot by 1 foot resolution. Each data tile was created utilizing multiple aerial images. Images were captured on the following dates in 2005: March 28, April 4, April 8, April 14, and May 4. Programmatic details for CUA data were outlined in Illinois GIS Notes, Winter 2005.

Data Distribution: Compressed Data

Compressed data are LizardTech's MrSID Generation 2 .sid files. Target compression ratio was 8:1; one compressed file is roughly 9 megabytes in size.

A statewide collection of both 2005 CUA data (40 Gigabytes) and 2005 National Aerial Photography Program (NAPP) data requires about 100 Gigabytes of storage space. We do not plan to distribute compressed data files by any other means (cd-rom, zip drives, portable drives, ftp download, etc).

CUA 2005 compressed data are available free-of-charge via:

all 6 UTM Counties (4,527 data tiles), or individually for Cook, Dupage, Kane, Lake, McHenry, and Will counties, or

all 6 SPE Counties 4,365 data tiles, or individually for Cook, Dupage, Kane, Lake, McHenry, and Will counties, or

an interactive map for data download and viewing.

    Compressed .zip file bundles contain:

<filename>.sid - compressed image

<filename>.aux - georeferencing information, associated with .sid image

<filename>.sdw - georeferencing information, associated with .sid image

<filename>.xml - metadata file for uncompressed GeoTIFF image, not edited for compressed image

Metadata:

Original USGS CUA 2005 Collection metadata

File indexes:

cua_isgs_indexes.zip - shapefile file indexes for the UTM and SPE projections.

Resources:

cua05archive.zip - data archive directories for the UTM and SPE projections.

UTM file naming convention based on the United States National Grid (USNG).

• Introducing the United States National Grid by Mike Price.
• How to Read a United States National Grid (USNG) Spatial Address

State Plane file naming convention based on data tile coordinates.

Data Distribution: Uncompressed Data

The ArcIMS interactive map was created for the Universal Transverse Mercator data by loading the original GeoTIFF files into ArcSDE.

Contact the Illinois State Library to obtain indiviual, uncompressed Illinois 2005 orthoimagery files. Note that one statewide collection of uncompressed 2005 CUA data (310 to 320 Gigabytes) and 2005 NAPP data would require about 1 Terabyte of storage space.

Project Support for Data Distribution

Project funding was contributed by: Illinois Department of Public Health, Illinois Department of Military Affairs, Illinois Environmental Protection Agency, the Federal Geographic Data Committee, and the US Geological Survey.