topic Re: Creating buffers dependent on polygon areas in Geoprocessing Questions

Creating buffers dependent on polygon areas

COLINGUILFOYLE — Tue, 09 Feb 2021 18:40:28 GMT

I'm trying to create buffers around polygons with the buffer distance dependent on the size of the polygon. For example, a polygon of <50 hectares would get a buffer of 100m, 51-199 hectares gets a buffer of 200m, and so on. I've been using the Create Buffers tool and trying to use an Expression buffer type. Firstly, I'm not sure if this is the best way to go about this so any advice would be appreciated. Secondly, my expression keeps failing due it not being valid (I'm new to Python).

The code I've been trying to input has been something like:

when($feature.Area_ha <= 50, 100,
($feature.Area_ha >= 51 && <= 199), 200,
($feature.Area_ha >= 200 && <= 299), 300,
($feature.Area_ha >= 300 && <= 399), 400,
$feature.Area_ha >= 400, 500)

If anyone has any advice on improving the code or another method that would be great.

Thanks !

Re: Creating buffers dependent on polygon areas

DavidPike — Tue, 09 Feb 2021 19:05:34 GMT

It's an Arcade expression rather than python (most similar to Javascript I believe)

I think you've missed supplying the variable again after each && (AND) statement, and also the default value if no conditions are met (in the below example I've supplied -99999)

when($feature.Area_ha <= 50, 100, ($feature.Area_ha >= 51 && $feature.Area_ha <= 199), 200, ($feature.Area_ha >= 200 && $feature.Area_ha <= 299), 300, ($feature.Area_ha >= 300 && $feature.Area_ha <= 399), 400, $feature.Area_ha >= 400, 500, -99999)

Re: Creating buffers dependent on polygon areas

COLINGUILFOYLE — Wed, 10 Feb 2021 08:43:55 GMT

Yes that's what the issue was - Thanks for the help!