Definition
A DOQ is a digital raster (pixel-based) image of an aerial photograph in which displacements caused by the camera and the terrain have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map. The digital image is rectified by processing each image pixel (picture element) through equations using ground control points that can be identified from photographs, camera calibration, and orientation parameters, and a digital elevation model (DEM).
Features and Uses
DOQs can serve as backdrops for vector data such as Digital Line Graphs (DLGs), Topologically Integrated Referenced Geographic Encoding and Referencing (TIGER) Line files and Soil Survey Geographic Database (SSURGO) files. Because of their consistent coverage of large geographic areas (statewide/regional coverages, service boundaries, transmission and distribution corridors, floodplains, watersheds, etc.) they are of benefit to the private sector, local governments, and regional planning commissions for resource management.
Map Scale/Resolution
The DOQ is either black and white (BW) or color infrared (CIR). It represents one U.S. Geological Survey (USGS) 7.5-minute quadrangle. The Digital Orthophoto Quarter Quadrangle, (DOQQ) represents one quarter of the quadrangle. The names are based on that of the 7.5-minute quad, followed by NE, NW, SW, or SE for the DOQQ. The DOQQ’s scale is 1:12,000 scale or 1"=1,000', with 1-meter pixel resolution, and accuracy of +/ 33 feet. Individual states may have DOQ's that have higher accuracy standards depending on additional post-processing.
Original Coordinate System
The standard quadrangle image is based on the Universal Transverse Mercator (UTM) coordinate system based on the North American Datum of 1983 (NAD83). Each image has between 50 and 300 meters of overedge to facilitate matching of adjacent images. See the documentation available at http://rockyweb.cr.usgs.gov/nmpstds/doqstds.html for a discussion of datum and projections used in DOQs.
File Formats
DOQs are available in three formats: Native, GeoTIFF, and MrSID. Native format is composed of BIL or BIP files, standing for Band Interleaved by Line and by Pixel, respectively. Further information on GeoTIFF software specifications can be found at: http://mcmcweb.er.usgs.gov/sdts/geotiff.html.
MrSID (for Multi-resolution Seamless Image Database) is used because DOQs are quite large - 50 Mb for the BW and 150 Mb for CIR. A DOQ in MrSID image files is less than 2 Mb at a 25:1 compression ratio.
How to Obtain This Data
The availability of DOQs in the United States can be located at: http://mcmcweb.er.usgs.gov/status/doq_stat.html. USGS offers Native and GeoTiff files on CD, DVD, and 8mm, as well as through File Transfer Protocol (FTP). To order DOQs online you will need to visit http://earthexplorer.usgs.gov. The price for a B/W 3.75-minute is $7.50 and $15 per file for a CIR. The B/W 7.5-minute is $15 per file. Ordering online includes a $5 handling fee and $30 base charge per order.
Ohio DOQs in MrSID format are available from OGRIP/GIS Support Center. These are available statewide. These files are projected to State Plane coordinates. Only black and white DOQs are compressed with MrSID format. You can obtain these files free of charge from
http://metadataexplorer.gis.state.oh.us/metadataexplorer/.
Data files are provided using a specific naming structure that includes: prefix + geodata type + FIPS zone + file extension (i.e., ca201se3402.sid or .sdw). To download the appropriate files for your location in Ohio you will need to read the doq_index.txt and 24k_idx.pdf file. Refer to the 24k_idx.pdf file and determine the map name within your county. Refer to the table within the doq_index.txt file and locate your county and the map name for the necessary FTP directory and prefix.
Use with Mapping and Viewing Software
Native, GeoTIFF, and MrSid formats can be read by most GIS Software. Two freeware programs for Windows 95/NT/2000 can read DOQs in Native and GeoTIFF format. These are DLGV32, available at http://mcmcweb.er.usgs.gov/drc/dlgv32pro/ and MICRODEM, available at http://www.usna.edu/Users/oceano/pguth/website/microdem.htm.
MrSID GeoViewer can be downloaded free of charge from http://www.lizardtech.com/.
Metadata Information
References
Documentation and sample images can be found at:
http://metadataexplorer.gis.state.oh.us/metadataexplorer/
http://mac.usgs.gov/mac/isb/pubs/factsheets/fs05701.html
http://www-wmc.wr.usgs.gov/doq/
http://mapping.usgs.gov/www/ndop/
Contacts
Earth Science Information Center U.S. Geological Survey 345 Middlefield Road Menlo Park, CA 94025 Telephone: (650) 329-4390 Fax: (650) 329-5130
