I have two DEM rasters from the USGS NED dataset. One is from 2013 and one is from 2017, the extents should, and appear to, be 100% identical. I ran the difference function on the ArcGIS Imagery Analysis window on these two rasters and got a resulting difference raster that appears to be accurate (via spot checking the input raster pixel values). However when I zoom out past a certain point the difference raster symbology becomes incorrect & in contradiction of the identified pixel va lues. (which remain accurate and in contradiction of the symbology) The left image is at 1:250000 scale, the right 1:30000. The error remains as I zoom out past 1:300000. Classified in the attached as: Black = no difference (within a small tolerance), red = values decreased, green = increased.
Any ideas why might it be doing this and how can I get it to stop? I'd like to get a single view of the entire difference raster but this problem is preventing that. One input raster was in .img format, the other .flt, and both were single band & in the same unprojected GCS.