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I got a temperature raster (maximum temperature for January, global extent) and the value range seems to go beyond the valid range. The highest is 42.006 (which I assumed should be Celsius) but the lowest is -9999 (which corresponds to the ocean). The image is attached.

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    It's likely that the -9999 value is a 'no data' value and this dataset doesn't include temperature data for the ocean.
    – jyingling
    Sep 3, 2019 at 20:06
  • The -9999 value is a placeholder for NoData. Sep 3, 2019 at 20:06

2 Answers 2

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You are looking at a NoData value. Taken from the ArcGIS documentation:

Cell values can be either positive or negative, integer, or floating point. Cells can also have a NoData value to represent the absence of data. Sometimes there are homogeneous areas in a raster dataset that the you do not want to display. These can include borders, backgrounds, or other data considered to not have valid values. Sometimes these are expressed as NoData values, although other times they may have real values.

If you want to change the color for the NoData pixels you have to specify it in the symbology as follows:

enter image description here

In case the NoData value is not set go to ArcCatalog or the Catalog window -> Right click on the raster -> Properties and Edit the NoData value.

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  • when i change the property "display NoData" it does not affect my raster in any way
    – user148822
    Sep 3, 2019 at 20:12
  • Did you change the color and click Apply? Sep 3, 2019 at 20:13
  • yes i did. it did not change anything
    – user148822
    Sep 3, 2019 at 20:23
  • I just edited my answer to show you how to edit the NoData value. Sep 3, 2019 at 20:31
  • This worked! Thank you!
    – user148822
    Sep 3, 2019 at 20:38
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Building on the above answer - make sure that -9999 is assigned as the NoData value for the raster dataset.

Go to Layer Properties > Source > NoData value

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  • It is not currently assigned and it cannot be changed from the properties window.
    – user148822
    Sep 3, 2019 at 20:25

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