A digital orthophoto is a digital 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. Data files must remain as small as possible while preserving image quality in a public domain file format that is common to imaging and GIS software.
Several formats are available from a variety of sources.
DOQQ images are being made available in this clearinghouse in the MrSid format. In the future DOQQ's will also be available here in the ER Mapper format. Many types of files meet National Map Accuracy Standards. The extent to which each format meets these objectives is still under evaluation. A viewer for MrSID files can be downloaded from LizardTech.