Zonal statistics as table does not produce appropriate results

JuliaLukyanets — Fri, 18 Mar 2011 18:52:24 GMT

Good afternoon

I have a polygon shapefile that I am trying to run zonal statistics on using your vert94eftfl.rtf GRID file.
When running zonal statistics as table in ArcMAP 9.2 we are using our polygon shapefile as an input feature zone data and your raster file as an input value raster.
Out goal is to generate an average value for each shapefile polygon using a raster file with values.

Raster file does not appear to have any "NO data" values in the domain we are interseted in, however, running zonal stats does not produce appropriate results. We are only generating values for 3 polygons out of 94 selected polygons. Why are we not seeing any values for the rest of the cells? There are definitely values there in the raster file. Zonal statistics only generates data for 3 cells out of 94 selected cells...? The problem is defintely with a raster file and not a shapefile (with polygons) that will have values fields from a raster file as a result fo zonal stats.

I am not an experienced GIS user but I was wondering if I am dealing with a certain type of a raster file that I need to do something else with prior to running zonal statistics.

Any help or input is really appreciated!

Thank you so much

Re: Zonal statistics as table does not produce appropriate results

JeffLee — Fri, 18 Mar 2011 21:45:42 GMT

Julia;

The problem may be due to using a too coarse raster for your polygons. For example, if only one cell intersect a polygon you may not get values as, if I am not mistaken, the centroid of a raster cell must be located inside the boundary of the feature for which you are making calculations.

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Zonal statistics as table does not produce appropriate results

Re: Zonal statistics as table does not produce appropriate results