In ArcGIS 10.1, I have two layers: 1) raster of Topographic Wetness Index 2) vector layer of polygons representing soil types

I am wondering how to accomplish what I am after, that is to get information for polygons from the underling raster. In other words, I would like to extract the mean TWI for each polygon in order to calculate what is (on average) the TWI for each soil type.


With the Spatial Analyst Extension, using Zonal Statistics as Table should give you what you need.

  • thanks for the prompt reply. May be my question was not clear. It is my understanding that extract by polygon will 'cut' the raster according to the polygons. What I am after is extract the mean value per each polygon from the underlying raster. Something similar to what 'add surface information' does in relation, e.g., to the polygons mean z (i.e., elevation). Instead of z, I would like to have the mean value of the TWI raster. I hope my poor English will not lead you astray. – NewAtGis Jun 20 '14 at 13:51
  • @Maksim you are right with zonal stat, but not with extract by polygon. You should edit your answer with your comment to make things more readable. – radouxju Jun 20 '14 at 14:04
  • @radouxju edited – Maksim Jun 20 '14 at 15:00

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