DOQQ

DOQQ- Digital Orthographic Quarter-Quads. These are aerial photographs that has been georeferenced
and orthorectified in order to remove distortions inherent to aerial photos, so as to transform them into accurate planimetric maps. DOQQs are smaller scale images, each covering one quarter of a quadrangle (four 1:12,000-scale DOQQs display the same area as one 1:24,000-scale DOQ), and are also raster formatted. In this orthophoto of an undisclosed river location, ground features are displayed in their true position, allowing for more accurate measurement of distance, areas, angles, and positions. Infrared imaging also provides greater contrast. Orthophotos are also useful because photos display features that may be omitted or generalized on maps, such as unofficial dirt roads and varying vegetation types in this case (http://www.geomart.com/products/geodata/doqq/index.htm).