Cartographers, people who make maps, produce orthophoto maps from aerial photos taken from a specially designed camera carried on a plane. In the United States, the U.S. Geological Survey coordinates aerial photography and the maps produced from the photos through several projects, such as the National Aerial Photography Program (NAPP) and the National High Altitude Photography (NHAP).
One main difference between an aerial photo and an orthophoto map is that an aerial photo shows perspective. The photographer can tilt the camera up and down to give the photo's viewer a sense of scale and height. An orthophoto map corrects for any camera tilt and removes any sense of perspective. For example, in an aerial photo a photographer can make skyscrapers look tall, but in an orthophoto map, they all look the same size -- you just see the building's roof from directly above.
When a cartographer creates an orthophoto map, through the use of photo manipulation programs, he removes the effects of camera or plane tilt and terrain relief from the map. Both these items distort the map's scale. By removing these effects, he creates a map that has uniform scale; that is, he creates a map that happens to look like an aerial photo. Like other maps, the end user can measure directly from the orthophoto without having to correct for distortion.
Unlike an aerial photo, a cartographer can overlay additional information on an orthophoto map. She can use the orthophoto as a source or background image in a geographic information system (GIS) or use it to review, revise or to collect more information on another map. She can also combine the information on the orthophoto map with Digital Elevation Models (DEMs) or Digital Raster Graphics (DRGs), which are scanned and georeferenced topographical maps.
Whereas an orthophoto gets used as either a map or in combination with GIS, an aerial photo gets used more when the photographer wants to show a different perspective of the Earth. Many building owners or real estate agents use aerial photography to show their clients an unusual view of the property. Some photographers and artists use kite aerial photography to show a different viewpoint than what people normally see.
- USGS: Maps, Imagery, and Publications
- USGS Western Region: Digital Orthophotos
- USGS Lake Tahoe Data Clearinghouse: Digital Orthophoto Quadrangle (DOQ)
- Oregon Explorer: More on DOQs
- Pennsylvania Spatial Data Access: Help
- University of California, Berkeley: Notes on Kite Aerial Photography; Charles C. Benton; June 2010
- Photo Credit Thomas Northcut/Photodisc/Getty Images
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