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I have a soil layer overlaying a watershed layer in ArcGIS Pro.

How do I calculate the different types of soil area within the watershed?

I have tried summarized within, but it does not work.

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    Intersect, calculate geometry (or field calculate the area), summary statistics
    – BERA
    Feb 12, 2021 at 8:04
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    hi Bera, thanks for your help. got it!
    – chaff
    Feb 12, 2021 at 20:47

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If you Union the two layers you will have a new layer with separate polygons for each combination of soil and watershed. As a simple example, three soil layers spread across two neighboring watersheds would results in six new polygons: SoilA_WaterA, SoilA_WaterB, SoilB_WaterA, SoilB_WaterB, SoilC_WaterA, and SoilC_WaterB.

You can then calculate the area of these new polygons in your union output using the Calculate Geometry Attributes tool (also available by right clicking in the attribute table). If you need to sum the area of multiple polygons (for example if there are three different patches of SoilA in Watershed A) use the Summarize Statistics tool.

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  • hi ycartwhelen, thank you for your explanation. I've tried your method, using 'Union' on the watershed and soil layer, there's a new column showing FID_Watersheds are -1, what does that indicate? Also, the attribute table looks quite similar to the original 'soil' layer table, i've sort of lost the watershed boundaries, will i be able to 'clip' it?
    – chaff
    Feb 11, 2021 at 19:22
  • I tried clipping it and I'm able to see clearly what type of soil is allocated to each watershed, but union exterminates that function.
    – chaff
    Feb 11, 2021 at 19:51
  • If you only have one watershed then clipping should work fine to cut out the sections of soil layer within the watershed from the rest of the soil layer. If you had multiple watersheds that FID_Watersheds column would give the ID number of each watershed, so you could differentiate between SoilA_WaterA and SoilA_WaterB. Or as @BERA suggests in the comments, you could use Intersect in place of Clip or Union. That might be a better option.
    – ycartwhelen
    Feb 12, 2021 at 13:09

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