3

EDIT: I am using Armap 10 sp 5 I have found similar questions but they were either unanswered or somewhat different to what I am asking.

I have a raster with cell values 1-5 and a polygon shape file with regular grid of squares the same size.

All I need as output is a table with the polygon ID and the raster value. I tried to use the zonal tool but in the option it does not have a weighted average based on the area that each raster cell occupies in the polygon grid cell. For example in a grid cell I might have two raster cells, one of value 2 that occupies 30% of the area and one value 5 that occupies 70%. My result would be 2*.3+5*.7=4.1 instead of 3.5 that I get with zonal tools.

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  • What GIS software and version are you using? Please edit that detail into your question and tags. – PolyGeo♦ Oct 11 '13 at 7:42
  • You're on the right track: Resample the raster to a finer cellsize (so that each polygon contains many cells) and try again. – whuber♦ Oct 11 '13 at 16:44
  • @whuber well that might be one solution, my grid is 10km, so what would be a fine enough cellsize? – Herman Toothrot Oct 12 '13 at 3:59
  • It depends on the accuracy you need. In my experience, resampling so that each polygon contains at least 100 cells is often good enough. – whuber♦ Oct 12 '13 at 22:22
  • @whuber ok I am trying your approach, however the zonal statistics doesn't go through and I get a few error messages. error in executing grid expression zonal statistics program failed, and also "the fields collection contained multiple oid fields" – Herman Toothrot Oct 13 '13 at 7:56

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