Summarize Within gives slightly smaller summary features' areas than acutal polygon areas

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12-20-2021 12:58 AM
JochemKail
New Contributor

I am using "Summarize Within" (ArcPro 2.7.3) to summarize the area of land use polygons having different land cover types in catchments of lakes. This means the input polygons are lake catchments, the summary features are land cover polygons having different land cover types, and the group field used is the code of the land cover types. The land use data for sure cover the whole lake catchments.

However, the sum of the area of the summary features given in the output grouped table is smaller and not matching the area of the input polygons!

For example, in the screenshot attached to this post, the catchment polygon MSCDLV_1100000 has an area of 1572268.24 squaremeters while the summarized area is only 1570380.6 squaremeters. Moreover, if I clip the land cover data manually using the lake catchment polygon, I can sum up the area of the land cover polygons belonging to the different land cover types, which gives me the correct results but the summed areas for these land cover types given by the Summarize Within tool are slightly smaller.

The only explanation I can think of is the following: The tool converts the summary feature layer to a raster and sums up all raster cells having their center located in the input polygon. This would results in somewhat smaller areas since the raster cells at the border of the input polygons would not be included. However, that would be "suboptimal" since it gives incorrect results. In former times, I had an ArcView Avenue script that calculated  summed areas by groups in input polygons. I hope I don't have to switch back to this one ;-).

Does anybody now - especially from the ESRI team - how the tool actually works and if this is the reason for the observed differences?

Many thanks!

 

 

 

 

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4 Replies
DanPatterson
MVP Esteemed Contributor
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JochemKail
New Contributor

Dear Dan,

many thanks for the quick reply. May I ask what you mean by "sort of retired"? The link says that the bug is known since version 2.3.2. I would have expected that such a basic tool will be fixed in the next update. Do you see any chance that this will be done in the near future?

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DanPatterson
MVP Esteemed Contributor

"sort of retired"  my signature and state

You should subscribe to the issue in the link.  There is a "Subscribe" button on the page and it upvotes the issue and you get notified of changes


... sort of retired...
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JochemKail
New Contributor

..."sort of retired" is a nice way of saying you are still helping people with ESRI software, thanks.

I already subscribed and got the notificatio. I am curious to hear if anybody else has a solution for this problem. If not, I will simply write a Python script, which would be an extra 1-2 days of work.

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