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I have a raster file with 5 classifications. I've calculated area for all of the classes via Zonal geometry, Arcmap 10. Now, I want to exclude patches which are smaller than 100 sq. km. and re-calculate the area for each class. Could anyone advise me how to do so?

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up vote 4 down vote accepted

Region Group on your original classified raster will identify 'patches' and assign them each a unique number in the VALUE field. Note: an item called LINK is added to the attribute table of the output raster, which indicates the original value for each cell from the input raster.

You can use the Zonal Geometry As Table tool again to get the area in map units OR the COUNT field times the cell size squared will give you area of the 'patch' (be sure to divide by 1,000,000 sq meters to get the output as sq kilometers) - Add/Calculate this to a new AREASQKM field in the attribute table.

Then select records where the AREASQKM > 100, and apply Summary Statistics using LINK as a case field and SUM AREASQKM as the statistics field and type.

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+1 Region Group is a great raster-based solution –  Aaron May 2 '13 at 15:38
    
There is an error while trying to use Summary Statistics; It says that OID is missing from the attribute table. I don't know how to fix it. –  Mahdieh Tourani May 3 '13 at 11:04
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What is the file format of your in_table? Summary Statsitics help indicates you can use "an INFO table, a dBASE table, an OLE DB table, a VPF table, or a feature class." Try exporting the attribute table to one of those types and then input to Summary Statistics. –  ccn May 3 '13 at 15:20
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