What is a digital orthophoto quadrangle (DOQ) or orthoimage?

A digital orthophoto quadrangle (DOQ) is a computer-generated image of an aerial photograph in which displacements (distortions) caused by terrain relief and camera tilts have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map.

Unlike an aerial photograph, a DOQ (or any orthoimage) has a uniform scale, so it can be used as a base map onto which other map information is overlaid. It is possible to measure directly on an orthoimage, just like other maps.

 

Air photo showing distorted path of pipeline as it crosses hills and valley, and orthophoto showing the true, straight path

Comparison of an aerial photograph and an orthophoto (orthoimage) from the Tenth Legion quadrangle in Virginia near the town of Arkton. The aerial photo shows a straight pipeline that is distorted by displacements caused by camera tilting and terrain relief (topography). The orthophoto removes the effects of tilt and relief and shows the true, straight path of the pipeline. Unlike the aerial photo, the orthoimage is a photographic map with a uniform scale. The orthoimage can be directly laid over other maps (and vice versa).

(Public domain.)