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Digital Orthophotographs on County CDs

Because of considerable data handling and storage issues with uncompressed digital orthophoto quads, the U.S. Geological Survey has produced compressed data for most users on county-formatted CDs. CDs with black and white DOQ images are now available for all Minnesota counties. 

Each county CD has two types of files for each quarter-quad image: a header record and an image file. The header file contains geographic information necessary to view the image. Unfortunately, the header file on the CD cannot be used directly with ARC/INFO or ArcView software packages and must be reformatted before the image file can be viewed. LMIC has developed a free program, called HEADER, to reformat each header file and is offering it via anonymous ftp or diskette. DNR's ArcView applications and EPPLviewer 2000 software, described below, also solve this problem. In addition, several of the published county CDs have image or header record errors. LMIC has compiled a list of known problem disks.

The decompression software provided on the USGS county DOQ CDs does not run under the Windows-NT operating system. To fix the problem, LMIC has recompiled the software and is providing it via FTP or diskette. From the FTP site, download both the djpeg32.exe file and the instructions, jpeg32info.txt.

The thumbnail image shows the northern portion of Como Lake and part of the golf course in St. Paul. The full image is 640x480 with a resolution of 1 pixel = 1 meter. This and other digital orthophoto quad images are best viewed with a monitor that can display images at 800x600 with 256 colors.

Related Sites

  • 2003 orthophotos from the Farm Service Agency are available statewide; 2002 orthophotos are available for 28 southern Minnesota counties.
  • Metropolitan Council's 2000 DOQs and 1997 DOQs for the seven-county Twin Cities metropolitan area
  • Minnesota DNR's ArcView Resources: Download custom applications for using DOQs with ArcView.
  • EPPLviewer: Download software to easily view and print DOQs from USGS CDs.
  • View and download nationwide DOQ images from Terraserver.
  • Download Minnesota DOQs from DNR:  resampled to 3 meter pixels and combined into full quadrangles.
  • Download Minnesota DOQs from LMIC:  resampled to 10 meter pixels and combined into county files.

Technical problems? Contact: demography.helpline@state.mn.us