Service Area Break Values Modified?

[CodyLyons]

I've been trying to perform a Service Area analysis using three break values (450, 900 and 1800) with both detailed and simple polygon generation in a model. The analysis produces the expected result using those break points when creating the detailed polygons, but the simple polygons don't. The process adds in other break points in addition to those requested.

I've copy/pasted the Detailed process and only changed the Polygon Generation to Simple.

Detailed Settings:

Simple Settings:

It would be less confusing if the Detailed process produced similar results, but it seems to work just fine. While I would love to know how to stop it, even knowing the cause of this or any advice you might have to avoid this would be fantastic.

Thanks for your time,

Cody

[MelindaMorang · Accepted solution]

This results from the NO_OVERLAP setting.  When you generate non-overlapping (or Split) polygons, the Service Areas get generated around each facility up to the point where it meets the Service Area polygon of another facility and then stops.  In the SIMPLE_POLYS case, the extra break values are indicating that those facilities didn't get all the way to the full extent of the specified break value before being truncated by the polygon from another facility.  If you switch to OVERLAP, this problem will undoubtedly go away.

I'm not sure why you don't see the same behavior for the Detailed case.  It seems like you should, but no doubt it's a quirk of the algorithm.  We have made some updates and improvements to the Service Area polygon generation algorithm in ArcGIS Pro, so I expect you would see more consistent results if you do your analysis there.

[CodyLyons]

Thank you for the reply and advice.

Like I said before: It's not so much that it's weird that it does that in Simple, or doesn't do that in Detailed, but more that it's weird that it doesn't stay consistent. And while that does answer why Simple Service Areas create new breaks, it doesn't answer why there is the difference between the two.

So I guess the question now flips: Why doesn't the Detailed Service Area process create new splits in the polygons?

We've been using Detailed Service Areas for years here, and we've never had it work like that. While it's been a while since I've performed Simple Service Areas, I can't recall it doing that in the past (but I could be wrong there, it's been a few months at least and we always use the Detailed polygons in the end).

I'll spend some time in both Desktop and Pro with the Service Areas and see if I can find a clue.