Issues with Intersect - How to calculate area of overlapping vectors?

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02-10-2021 05:33 AM
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amp2311
New Contributor

Hi there! I'm working with the London TfL hex grid (a uniform hexagonal grid geography created by the Transport department which spans the greater London area) and I'm trying to calculate the percentage of the area of each hex that is covered by a specific type of land cover. However, I'm running into major trouble using the methodology I'm familiar with because the landcover dataset I'm using is a very complex feature class (though it only includes two types of landcover). 

I dissolved the land cover dataset so it wasn't split into so many pieces (it dissolved into larger blocks of its two landcover types), which took nearly 8 hours to process. I then tried to intersect the landcover dataset with the uniform hex grid, which I would have then spatial joined to the hex grid and summarized the area of the intersected landcover dataset pieces (then, I could have divided the summarized area by the uniform area of the hexes to get a percentage). The Intersect tool ran 8+ hours overnight, and in the morning, returned a blank feature class, despite showing no error. 

Is there a different tool or methodology I could use to yield the same results? I have no other option in terms of land cover dataset- I've even tried simplifying the dataset, which also took hours to process and failed. If you have any suggestions for work arounds or other tools I might be unfamiliar with, PLEASE let me know!! Thanks!!

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DavidPike
MVP Frequent Contributor

Tabulate Intersection (Analysis)—ArcGIS Pro | Documentation should do the job.  I'm not sure if it will work as expected if you have multipart features though, so ensure you haven't inadvertently created multipart features from the dissolve tool (should be a little checkbox from memory).  Out of interest are these the hex bins for the environmental dashboard?

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amp2311
New Contributor

Hey there! I tried Tabulate Intersection and it ran for 10 hours then failed due to an unidentifiable error and produced a blank table (the only thing I'm seeing in the results window is "Tabulate Intersection [000000_12301899]", no error number or anything). Any idea why this could have happened, or any suggestions for alternate methods? 

It is the Hex grid that is used in the GI Focus map!

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DavidPike
MVP Frequent Contributor

Hi,

The first step would be to take a small subset of each datasource and trial the tool on that small sample area to see if it works.  If so, I think that leads to the size and complexity of the datasets being the issue.

This may lead to having to batch the hexagons into multiple processes (shouldn't be too difficult) if it is possibly a memory issue.

Try doing the same process in ArcGIS Pro if possible.

Simplify the geometry of the input features.

I'd also say to start a new post stating you have an issue with this specific tool, these were your inputs etc . lay it all out.

Are you using the tool to calculate any other metrics, and could you possibly share a screenshot of the tool inputs, and the error (or lack of) message.

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