Orthophotography combines the image characteristics of an aerial photograph with the geometric qualities of a map. Unlike a typical aerial photograph, distortions due to relief displacement (hills, stream valleys, buildings), camera lens, and aircraft attitude have been removed so that all ground features are shown in their correct ground positions. This makes a true image map possible and permits direct measurement of distances, areas, angles, and the detailed portions of ground features that are typically omitted or generalized on traditional maps. In a digital format, orthophotography fulfills a fundamental role as a geometrically accurate base map.
Digital Orthophoto Quadrangle (DOQ) data are useful to government, academia, and the private sector in many disciplines. As an excellent geographic base data layer, DOQs may be used for many large-scale mapping projects such as: urban planning for smart growth, environmental assessment, crop science, agriculture, geology, soils science, watershed management, geography, landscape architecture, civil engineering, biology, and pollution prevention.
Application of DOQs to local and regional problems enables more intelligent assessment and management of available natural resources and the man-made environment. As the most current imagery available, DOQs provide an excellent benchmark to explore historical trends including urban growth, land use, and erosion.
The U.S. Geological Survey National Mapping Division is the primary federal agency responsible for producing USGS DOQs at the national level. DOQs are coincident with the USGS 1:24,000-scale (1 in. = 2000 ft.) topographic quadrangle coverage, have been geometrically corrected to conform to a standard cartographic map projection, and possess a half x half meter ground spatial resolution The statewide National Aerial Photography Program (NAPP) is the primary imagery source used to produce DOQs.
DOQs depict physical and cultural features in far greater detail and are more current than published USGS quadrangle maps. DOQs can be readily combined with existing, older quadrangle map information in a GIS to produce an updated map of a desired geographic area.