National Digital Orthophoto Program
The National Digital Orthophoto Program (NDOP) was chartered in 1993 as a consortium of Federal agencies with the purpose of developing and maintaining national orthoimagery coverage in the public domain by establishing partnerships with Federal, State, local, tribal, and private organizations.
At one time imagery from the National Aerial Photography Program was the source for almost all Federal digital orthoimagery products. Now, imagery sources can be NAPP, Napp-like, NAIP, High Resolution, or from other sources and be either film or in digital format.
The digital orthophoto quadrangle (DOQ) is the standard product for the initial national orthoimagery coverage. The DOQ is 1:12,000-scale, quarter-quadrangle centered, and 1-meter pixel resolution. DOQs are cast on the Universal Transverse Mercator projection from black-and-white or color-infrared photographs. Each DOQ has an ASCII keyword header containing descriptive information about the image data, including photographic source type, date, software systems used to create the DOQ, and the production date of the digital elevation model metadata used in the orthophoto rectification process.
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.
A DOQ can be used on-screen to collect, review, and revise other digital data, especially digital line graphs (DLG) and topographic maps. When the DOQ is combined with other digital products, such as digital raster graphics (DRG) or digital elevation models (DEM), the resulting image provides additional visual information for the extraction and revision of base cartographic information.
Page last updated: Dec. 13, 2016