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enter image description hereWhen I reproject a raster in ArcMap using the project raster function (details in the image above) to change its X,Y coordinate system from North_America_1983_Transvers_Mercator to NAD_1983_Idaho_TM, the values in the result raster tend to increase than the original raster values. How can I fix this?enter image description here

PolyGeo
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Atiqullah Atif
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    Please [Edit] the Question to provide the exact details of how you did the reprojection. Depending on the parameters used, such a result is certainly possible, and probably correct (due to extrapolation). – Vince Feb 03 '21 at 04:45
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    Did you use cubic resampling? Cubic resampling causes funny artefacts where there are sharp changes. If not can you include the parameters used by your raster projection (hint: have a look at your results tab https://desktop.arcgis.com/en/arcmap/10.3/analyze/executing-tools/using-the-results-window.htm ). Did you calculate your statistics on BOTH rasters? If not the values shown are estimates. – Michael Stimson Feb 03 '21 at 04:47
  • @MichaelStimson Yes, I calculated the statistics on both rasters and they seem to be fine. Nothing abnormal. And I used the NEAREST resampling technique. You can see the details in the image now. – Atiqullah Atif Feb 03 '21 at 05:01
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    Now that is weird, nearest isn't supposed to change the values, the same with majority. Can you classify lower than expected, in range and higher than expected then polygonize the ranges to locate the areas of change? You'd need a spatial analyst license to do this in ArcGIS but it can be done in QGIS efficiently https://gis.stackexchange.com/questions/17712/performing-raster-reclassification-in-qgis then having both rasters and polygons go to the areas of 'outside range' and confirm that the pixel values have changed. – Michael Stimson Feb 03 '21 at 05:23

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I was having this same problem with a USGS DEM because I failed to set the "Source CRS [optional]" in the QGIS Warp (Reproject) form. I was getting values (elevations) about 7% lower than they should have been.

I needed to set the source CRS to the original DEM projection (EPSG:26912 - NAD83 / UTM zone 12N). I described my problem and this solution in this question: Reprojecting (warp) raster changed the values of the reprojected raster QGIS

This could be your answer.

Tom Haws
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    You have posted this answer several times, but the linked question has no answers. Please explain "I described my problem and this solution in this question: Reprojecting (warp) raster changed the values of the reprojected raster QGIS" – MrXsquared Jul 27 '23 at 20:16
  • This question is about ArcMap but your answer is about QGIS. In any event please do not post the same answer on more than one question. Doing so suggests that the questions may be duplicates suitable for merging. – PolyGeo Jul 28 '23 at 07:50
  • My apologies about the ArcMap mismatch. My blunder. I added an answer at the linked question. Let me know if I need to change anything else. – Tom Haws Jul 28 '23 at 22:53