{ "culture": "en-US", "name": "", "guid": "", "catalogPath": "", "snippet": "The Northeastern Illinois Planning Commission contracted for aerial photography every five years beginning in 1970 to monitor the distribution and change of land use in the region.", "description": "

The project involves scanning of the CMAP\u2019s collection of historic aerial photography for 6 counties (Cook, DuPage, Kane, Lake, McHenry and Will) in Northeastern Illinois, and georeferencing them for archival purposes, GIS-friendliness and public access through the CMAP website. Photos of the region were generally taken every five years, beginning in 1970, and printed on large Mylar sheets, which have limited usefulness in the age of GIS and open data. The scanning and georeferencing is an ongoing project, which began in 2013 with the photographs from 1995. This document pertains to the procedures used for that set, and the technical issues encountered.<\/SPAN><\/P><\/DIV>", "summary": "The Northeastern Illinois Planning Commission contracted for aerial photography every five years beginning in 1970 to monitor the distribution and change of land use in the region.", "title": "Historical Aerial Photography: 1970", "tags": [ "Cook", "DuPage", "Kane", "Lake", "McHenry and Will", "Northeastern Illinois", "black and white", "aerial photography" ], "type": "", "typeKeywords": [], "thumbnail": "", "url": "", "minScale": 625000, "maxScale": 5000, "spatialReference": "", "accessInformation": "Chicago Metropolitan Agency for Planning (CMAP)", "licenseInfo": "

While the images are georeferenced, they are not orthorectified. Orthorectification is a process that incorporates elevation and image sensor data to correct for distortion in the image caused by irregular terrain, camera tilt, and other factors. The georeferencing process described elsewhere on this page gets the imagery \"in the ballpark,\" and is best suited for the qualitative assessment of historical land use patterns at a scale of 1:10,000 or higher. While there has been no formal assessment of spatial accuracy, variances of 50' or greater have been observed in some locations when compared with orthorectified imagery.<\/SPAN><\/P>

These images are scans of half-tone enlargements, and not of the original (continuous-tone) prints nor of the original films. An unavoidable byproduct of using a digital scanner on half-tone prints is a patterning known as moiré that is visible at certain scales. While the resultant image is considered unacceptable for engineering, remote-sensing, or other technical applications, this is the best available in the absence of the original photographs.<\/SPAN><\/P><\/DIV>", "portalUrl": "" }