Digital Orthophoto Quadrangle (DOQ)

A Digital Orthophoto Quadrangle (DOQ) is a digital, uniform-scale image created from aerial photos. It is a photographic map in which ground features are displayed in their true ground position because relief displacements caused by the camera and terrain of an aerial photograph have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map; thus, it is possible to get direct measurements of distances, areas, angles, and positions from a DOQ.

What is the difference between an aerial photograph and an orthophoto?

1. A conventional perspective aerial photograph contains image displacements 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. It is not a map.
2. The effects of tilt and relief are removed from the aerial photograph by a computer rectification process to create an orthophoto.
3. An orthophoto is a uniform-scale photograph. It is a photographic map.
4. Since an orthophoto has a uniform scale, it is possible to measure directly on it like other maps.
5. An orthophoto may serve as a base map onto which other map information may be overlain.

For more information about DOQs, please visit http://craterlake.wr.usgs.gov/doq_brief.html.

DOQ Download

A standard DOQ is distributed in a quarter section of a standard 7.5-minute quadrangles. The one meter resolution of the DOQ results in a very large file size. Each quarter quadrangle DOQ is ~50MB; the complete mosaicked DOQ for the Lake Tahoe Basin is ~3GB.

DOQs are often compressed with JPEG compression, but for distribution here, all the DOQs for the Lake Tahoe Basin have been mosaicked together and compressed with MrSID compression from LizardTech. The compressed MrSID file has been reduced from ~3GB to ~144MB, which is still too large for convenient download over a modem. Viewers are available for free from LizardTech on their website.

Patterns in the lake is an artifact of the camera.

DOQs are in UTM NAD83 zone 10 projection. Raw (original) data are in the following projections: data east of 120 degrees longitude are in UTM zone 11 and data west of 120 degrees longitude are in UTM zone 10. It is not possible to combine different UTM zones in Geographic Information System (GIS), therefore, all data have been reprojected into one standard projection, UTM NAD83 zone 10 projection, for the Lake Tahoe Basin. DOQ mosaics of the Lake Tahoe Basin: DOQ for 1992 (MrSID and world file, 141 MB compressed). DOQ for 1998 (MrSID and world file, 123 MB compressed). Metadata -- Original -- Reprojected