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I am using ArcGIS 10.2. Whenever I reclassify a raster layer I get the following message:

Unique values cannot be obtained from raster, using values from dialog

This does not prevent from proceeding with the reclassification. I found that if I convert the data to integer prior to reclassification, I do not receive this message.

However, I do not want to convert all my data to integer, especially since I am using data which is represented by values of less than one, hence needing the additional step of multiplying the rasters by 1000 before integrating them.

What does this error message mean? Can I just ignore it? Does it affect the accuracy of the reclassifications?

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From ESRI support: Increase the maximum number of unique values allowed in a raster attribute table

Try setting the maximum number of unique values to one greater than the number of cells in the raster dataset; I suspect it will go away.

  • In ArcMap or ArcCatalog, click Tools > Options. (In ArcGIS 10, click Customize > ArcMap Options.)
  • Click the Raster tab.
  • Select the sub-tab named Raster Attribute Table. (In ArcGIS 10, it is on the Raster Dataset sub-tab.)
  • Increase the maximum number.

I do not think it alters the reclass one iota. Just an annoyance.

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    It means the actual output will be identical even if you do the "fix". Nothing changes is the most likely scenario but the message may go away. – If you do not know- just GIS Dec 22 '15 at 13:59

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