Why do the maximum of the value change when I use set null function in ArcMap

235
4
01-10-2021 10:29 PM
YiqianZeng
New Contributor

I want to set null to the value<=0 using the raster calculator in ArcMap(the original raster value is -3000 to 10000), but after that, I got a new raster with a changed maximum value (the new raster value became 1 to 9987). Is there any problem with my setting? How to keep the other value (e.g. maximum value) the same but set null to value<=0?

0 Kudos
4 Replies
DanPatterson
MVP Esteemed Contributor

Are you relying on the symbology in the table of contents to ascertain the minimum or maximum values of the before and after rasters? or did you determine the actual statistics?  Don't use symbology values, use the actual statistics.

Also, what did you do to ensure that the output raster retained the exact same extent and cell size during the operation?


... sort of retired...
0 Kudos
YiqianZeng
New Contributor

Thank you for your reply. I check the range of values in the raster data from the table of contents as it shows the minimum and maximum values for the raster data. So how can I obtain the actual range value of the raster data and where can I look for it? 

I set the spatial reference before adding the raster data and then use the raster calculator to set null to a value less than 0, but I am not sure this operation can retain the same extent and cell size or not. Could you give me some tips? Thank you.

0 Kudos
DanPatterson
MVP Esteemed Contributor

right click on the layer, select Properties, Source and Statistics... you will see the min max etc


... sort of retired...
0 Kudos
YiqianZeng
New Contributor

Thank you for your reply. I check the range value of the original layer according to the operation you mentioned before using the set null function. It shows no value in the statistics part (including min, max, mean, std dev). However, after doing the set null function, it shows the min and max value the same as what it is shown in the table of contents. What else can I do to check the actual range value of the original layer? Hope for your reply, thank you.

0 Kudos