Summarize Within - "Summarized Area in Acres" inconsistent measurement

Question

Hi,

I am using the Summarize Within analysis to analyze the 'Land in Crop' and "Total Farm Area' within 50km buffer of specific towns. When I review the data, the area in KM2 is consistent with the area of a circle zone of 50km radius, however the Summarized Area in AC is different from town to town. Should it not be reflective of the total area measured or is it measuring something else?

Input Feature: Canada Census of Agriculture 2021

Summary Area: 50km buffer layer (created)

Measurement: Sum of Land in Crop and Sum of Total Farm Area

AmandaRing · Answer

Hi @uniuni,

As @Neal_t_k mentioned, the "area" fields in the output of the Summarize Within tool reference different things:
A) Area in Square Kilometers - this is the area of the summary polygon, which in your case is the buffers around your cities, and should be consistent, as you mentioned
B)Summarized Area in Acres - the key word here is "Summarized"; this the amount of area within each polygon covered by your input features, which in this case, is the Canada Census of Agriculture 2021 polygons. If that layer fully covered all of North America, including water features, then all polygons would have the same value, which should match the area of the polygons (stat A). But since the Canada Census of Agriculture 2021 features don't cover the full area, the value will change within each buffer. Consider Buffer A and B in the image below:

Buffer A will have a smaller Summarized Area in Acres than Buffer B, because the top part of the circle does not contain any polygons from Canada Census of Agriculture 2021 (where the dark grey basemap is what's visible), whereas Buffer B is fully covered by features with varying values.

You can either turn off returning this value, or change its units, using these controls:

PS - if you are doing this workflow again, I would suggest using the Summarize Nearby tool to combine the two steps of your workflow into one; you can use your city points as the nearby features around which to draw a buffer that the tool will then summarize the values into:

This will return the same results as your Create Buffers > Summarize Within workflow.

I hope this helps! Let me know if you have any further questions.

Cheers,

Neal_t_k · Answer

Looking at  Canada Census of Agriculture 2021 feature layer , the polygons don't cover 100% of the area your buffers do, so it is only adding up the area of the polygons within your buffer.

No polygon in red, so that area is not part of the calc.