Digital Orthophoto Quadrangles (DOQs) or Digital Orthophoto
Quarter Quadrangles (DOQQs) are aerial photographs that are in an electronic
format. The most common format is a MrSid file. These files can be
viewed with a viewer from
LizardTech. Keep in mind that the image has been reformatted for
topography and camera distortions so that distances are accurate. To
read more about DOQs see
http://www-wmc.wr.usgs.gov/doq/