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I have selected certain values in a raster (roughly 1000 cells), and would like to export them to be able to create a polygon. Converting it to points first then to polygons does not work. Can anyone suggest a better method?

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2 Answers 2

If you use the set null tool in the spatial analyst toolbox to assign a null value to any raster cell not in your selection you will be able to perform a raster to polygon conversion on the result.

This should give you the polygon(s) you need.

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I've taken a look at the Set Null tool, and I see it asks for two rasters, not just one. – Cindy Williams Sep 4 '12 at 8:48
It asks for a False raster or constant value, so you have the choice of putting a null value in as a constant (eg -9999), or use your input raster as the as the false raster and invert your selection. – sgrieve Sep 4 '12 at 8:53
Setting nulls is a good idea but it's really peripheral to the core issue: you need also to convert the selected cells to a constant integer value for the conversion to work. Thus, for instance, if the cells have been selected by means of some logical condition cond, then the raster calculator expression cond creates a binary 0-1 grid which, when converted to polygon, yields two components: one for the selected cells and another (which can be deleted) for all other cells. – whuber Sep 4 '12 at 12:42
@whuber I used the con tool on the input raster to perform the operations which you described, it worked perfectly! Thanks – Cindy Williams Sep 6 '12 at 8:06

To make this an official answer with more detail: I was able to do this with the con tool as Cindy mentioned.

  1. With the raster cells you're interested in selected, open the con (Spatial Analyst) tool.
  2. Use your original raster dataset as both the input conditional raster and true raster.
  3. Select an output raster name and location.
  4. Click ok.
  5. The output is a raster dataset, but with just your selected cells. From here you could convert the output to polygon if needed.
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