Seams or discontinuities in a composite elevation file will occur due to differences in the
quality and accuracy of the input DEM data files.
These seams must be corrected or minimized to provide the user with data useful for a range of applications. Seams generally arise when spikes or an offset occurs in elevations values between two DEM data files. An edge matching operation is used to detect spikes or offsets along a seam. If a spike is found the bad elevation is replaced by an bilinear interpolated value. If an offset is found the edge-matching algorithm forces the DEM to fit along the edge, respecting slope continuity, and distributes the residuals of any mismatch outwards from the seam in an inverse-distance-squared fashion. The magnitude of the residuals will range from a few meters up to 60 meters. (courtesy of the USGS) | 
