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I need to work out how much tree cover is in a polygon. The tree/vegetation layer is a raster with non-integer values for height (the Environment Agency VOM data if anyone's familiar). Height values for the VOM range from 0 (bare-ground) to 46.942m (tallest trees). My polygon layer is a 10 meter buffer around the Detailed River Network (a polyline layer of rivers in England). When overlain, they look like this:

enter image description here

As you can see, the green pixels are representing trees/vegetation and their height.

I am trying to find out how much of the shaded area is covered by trees. Ideally, I would be able to set a threshold for height (2.5m say) and calculate the area of the polygon covered by pixels with greater values than that threshold.

Does such a tool exist?

Apologies if this is a really straightforward answer.

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You can use the CON() tool to select pixels that are greater than 2.5 in value, the trick is to set the Mask environment setting to the polygon and ensure cell size is the same as your input VOM raster.

This will create a new raster with those pixels coded to the True value, usually you set it to 1. Then it is a simple count of the pixels multiplied by pixel area.

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