SOM is a space-based map projection in which the reference meridian nominally follows the spacecraft ground track. It provides a mapping from latitude and longitude to a coordinate system that is approximately aligned with the MISR swath. SOM was used because it minimizes distortion and resampling effects, and permits the greatest flexibility in the choice of Earth-based projections. SOM also allows direct cross-comparison with data from other instruments and simplifies global mapping, since the data have already been geolocated. For more information see the MISR Level 1 Georectification and Registration Algorithm Theoretical Basis Document (link is external) (ATBD-MISR-03), and also Snyder, J.P., Map Projection – A Working Manual, United States Geological Survey Professional Paper 1395, U.S. Government Printing Office, Washington, DC (1987). Source.