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I have a raster dataset created from the pixel classification of a satellite image. The pixels have 4 possible values, representing different land cover classes : 1, 2, 3 and 4. Using ArcMap 10,4, The display works fine, as you can see in the first image. enter image description here

However, when looking at this raster's properties wanting to change the colors to something "land-cover-ish", the minimal value of the file is not 1, but rather 1,33244 (see image below). I am therefore unable to display the 4 different classes, neither to perform zonal statistics as I intended to do. enter image description here Strangely enough, the four classes appear as expected in QGIS.
Has anyone stumbled upon this issue?

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It looks like it is just the way the Sybmology Classifier is assigning values to the cell ranges. You have 4 values in the range and 3 classes specified in the symbology classifier. The default is the "Natural Breaks (Jenks)" classifier, which will be trying to divide you 1 to 4 range into 3 classes, so that the variance between the 4 classes is kept to a minimum.

You have some options:

To change the display of the raster (for mapping):

1) Click the "Classify" and then choose how many classes you want. Then manually type in the break ranges in the right-hand column with the range values. 2) Click the "Unique Values" option to show all 4 classes and then merge the classes manually in the symbology editor window.

To change the actual range of cell values in the raster itself (for an processing you wish to do):

1) You can use the "Reclassify" Tool in the Spatial Analyst Toolbox to change the actual cell values in the raster based on how you want to split the range of data values in the raster dataset.

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  • Thanks for your answer! Still cant get it to work... ArcGIS shows the smallest value of the raster dataset to be 1.33, not 1. I therefore cannot classify it manually. – LandryF Aug 23 '18 at 13:22
  • @LandryF - When you selected the "Unique Values" in the Symbology Tab, what values were shown? – Keagan Allan Aug 23 '18 at 23:32
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So, I found a workaround, if it may be called so...

The raster showed properly in QGIS, with the minimal value as 1 (not 1.33). I could easily change the display colors for each land cover class.
enter image description here

As for the zonal statistics I wanted to perform, I used the 'Rasterstats' plugin instead of ArcGIS 'Zonal histogram' tool.

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