How does photogrammetry turn aerial and satellite photographs into maps?

Photogrammetry is the science of using photographs to create accurate maps and surveys. Because aerial photographs are not maps—due to distortions like radial displacement and terrain relief—photogrammetry employs specific techniques to translate photographic data into precise cartographic representations.12

The process generally involves these steps:

• Establishing Control: A framework of ground-control points is identified to provide known locations and elevations, which are used to scale and orient the photographs.12
• Creating Overlaps: Cameras capture images in strips with significant overlap (typically 60 percent). This allows features to be viewed from multiple angles.2
• Stereoscopic Modeling: By viewing consecutive overlapping images through a stereoscope or specialized plotting instrument, operators create a three-dimensional model of the terrain.2
• Plotting and Contouring: Using mechanical, optical, or computerized analytical instruments, the operator traces features and plots contours. Modern computerized systems can measure coordinates on photographs and perform the conversion to a three-dimensional model automatically.2
• Orthorectification: For high precision, devices like an orthophotoscope scan the overlap to produce an orthophotograph, which corrects scale distortions across the image.2