Nevada DOQs (FTP Link)
Digital Orthophoto Quadrangle (DOQ)
The Keck Center has approximately 10,000 DOQs for Nevada, including 3.75 minute (quarter quad), 7.5 minute (quad), and 30 minute (64 quads). All DOQs are geo-referenced in NAD 1983 UTM Zone 11.
The 3.75 minute DOQs are in .tif format and are provided through the courtesy of the U.S. Bureau of Land Management.
The 7.5 minute DOQs are in Mr.Sid format and are mosaics based on the four 3.75 minute quarter quads. The 30 minute DOQs are in Mr.Sid format and are mosaics based on sixty-four 3.75 minute quad DOQs. The 7.5 and 30 minutes DOQs were provided through the courtesy of the Nevada Bureau of Transportation.
An aerial photograph and an orthophoto or orthoimage may look alike but there are several important differences that allow an orthophoto to be used like a map. A conventional perspective aerial photograph contains image distortions caused by the tilting of the camera and terrain relief (topography). It does not have a uniform scale. You cannot measure distances on an aerial photograph like you can on a map. An aerial photo is not a map. The effects of tilt and relief are removed from the aerial photograph by a mathematical process called rectification. An orthophoto is a uniform-scale image. Since an orthophoto has a uniform scale, it is possible to measure directly on it like other maps. An orthophoto may serve as a base map onto which other map information may be overlaid. The preceding description is from the USGS DOQ page.