Zonal statistics as tabel - missing zones

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11-20-2013 11:19 AM
StefanieSteinbach
New Contributor III
Hi all,
A lot has been posted about missing zones using this tool, but I could not find anything useful for my problem.
I have derived about 200 subcatchments from a dem and converted them to polygon. After using zonal statistics as table to get a mean value for slope and the topographic wetness index within these zones a whole lot of zones is missing; the others are calculated as usual. Does anyone know what the problem could be related to?
Any hint is much appreciated.
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2 Replies
EricRice
Esri Regular Contributor
Hi Stefanie,

It's most likely related to the zone size.  From the help system:



  • If  the zone input is a feature dataset with relatively small features,  keep in mind that the resolution of the information needs to be  appropriate relative to the resolution of the value raster. If the areas  of single features are similar to or smaller than the area of single  cells in the value raster, in the feature-to-raster conversion some of  these zones may not be represented.

  • To  demonstrate this, try converting the feature dataset to a raster with  the appropriate feature-to-raster conversion tool and specify the  resolution to be that of the Value raster. The result from this  conversion will give an indication about what the default output of the  zonal operation will be.
    If  you have fewer results in the output than you may have expected, you  need to determine an appropriate raster resolution that will represent  the detail of your feature input, and use this resolution as the Cell Size of the Raster Analysis Settings of the Environment.


Best,
Eric
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StefanieSteinbach
New Contributor III
Hi Eric,
Thanks for your reply. However, this is not the problem as I used the zonal statistics tool before with smaller polygons and got complete values. Is there a workaround?