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I have a Watershed with ~100 smaller watersheds as a shapefile. I want to count the number of different land use values (they are in a 30x30m raster) in each of the small watersheds.

I tried combining them but nothing turns out they way I need it. Which tool or routine can I use to get this?

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  • The best tool for that is tabulate area. Make sure to set environments.variables cell size and snap raster equal to ones from landuse raster. – FelixIP Dec 2 '17 at 4:44
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One of the powerful tools in ArcGIS is the Tabulate Area tool, which allows you to calculate the area of each land use within each polygon in the polygon shapefile (watershed in your case).

The output will be a table that computes the area of land use in each polygon. If you want to know the number of pixels of land use simply you can create a new column and divide the area by 900 (30 x 30) and you will get the number of pixels of land use within each polygon.

Spatial Analyst extension is required to use Tabulate Area tool.

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If the smaller watersheds are in the same shapefile as the larger watershed, select and save the smaller watersheds as a separate shapefile. Run the Zonal Statisticstool with Variety as the target statistic. Your output should be a raster with the number of unique landuse values in each zone (small watershed) assigned to cells within the zone. You could explore [Zonal Statistics as Table][2.

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There is a specific tool for your problem. It is called zonal histogram. You will use small watersheds as input feature and land use raster as input value raster. Then it will create a table that shows different land use counts as pixels for each watershed.

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    Underrated answer. I've been searching for this functionality for sometime in QGIS. – Lisa May 8 '19 at 23:17

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