How do I fill in the blank areas where streets are far apart?

Question

Hey Yall,

Its been a while since I've used network analyst and I seem to be having a problem with the service areas leaving chunks of blank space in rural parts of town where the streets maybe a mile apart.

I have adjusted what seems like everything and it doesn't seem to make any difference and I don't remember this being a problem the last time I used it. I attached a picture for reference, any help is greatly appreciated.

Thanks!

Network Analyst.png

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Melinda Morang · Answer

The Polygon Trim Distance setting is the one that influences how far back from reachable streets polygons should be generated.  Here's the documentation for that: https://doc.esri.com/en/arcgis-pro/latest/help/analysis/networks/service-area-analysis-layer.html#426

From your screenshot, I'm guessing you're using ArcGIS Pro 3.6 or higher and the option to split polygons between facilities.  For the ArcGIS Pro 3.6 release, we rewrote the split polygons algorithm to make a couple of key improvements:

* Make it so large swaths of unreached areas between polygons is no longer covered
* Clean up small areas of overlap along boundaries
* Improve performance

In previous releases, we had a problematic scenario that produced inaccurate service area polygons.  When you used the split polygons option and had multiple facilities surrounding a central hole - an area not reachable by any facility within the time or distance cutoff - that hole was getting covered over.  This result was inaccurate because that area is NOT reachable within the impedance limit, so the results were misleading.

For your case, I think the lack of road density is making it look a bit worse along the boundaries between the area covered by your different facilities.  You can increase the polygon trim to improve upon that.