topic Trouble with Service Area polygon size in ArcGIS Network Analyst Questions

Trouble with Service Area polygon size

SteveTaylor2 — Wed, 29 Aug 2012 08:00:06 GMT

Hello,

I've had a look at previous threads discussing this issue but the solutions suggested on those threads have not seemed to help with the problem I have.

I have set the Service Area Polygons to distances of 5, 10 and 20 miles from my locations (using the equivalent number of meters - 8047m, 16093m, 32187m) but the result is confusing. As you can see in the picture there is very little difference between the 5mile and 10mile polygon in the North-East direction despite roads existing there. Also I measured the 20 mile polygon distance using the green route (applied to the same network) but the route measures 12.5miles yet reaches the edge of the 20mile polygon boundary?

[ATTACH=CONFIG]17312[/ATTACH]

Can anyone explain why this is? In previous threads creating a route on the network was suggested to identify broken links but in this case the route is fine but the service area is incorrect?

Thanks for your time,

Steve.

Re: Trouble with Service Area polygon size

JaySandhu — Thu, 30 Aug 2012 15:07:55 GMT

Most likely there is a high cost street in that area. Bring up the properties of the service area layer and turn on the Lines and have it split lines at breaks, re-solve. Now examine the lines in the area of interest to see what is the cost assigned to the edges (from/to cummulative costs). That should point to the underlying network costs causing a distortion in the polygon.
Jay Sandhu

Re: Trouble with Service Area polygon size

SteveTaylor2 — Fri, 31 Aug 2012 07:44:49 GMT

Most likely there is a high cost street in that area. Bring up the properties of the service area layer and turn on the Lines and have it split lines at breaks, re-solve. Now examine the lines in the area of interest to see what is the cost assigned to the edges (from/to cummulative costs). That should point to the underlying network costs causing a distortion in the polygon.
Jay Sandhu

Thanks very much for your help Jay. When using the line generation it prompted me to turn off the hierarchy I was using (I numbered motorways, A roads, B roads and minor roads 1-4) and the polygons look correct now. As I'm only interested really in distance, not time I'll not use the hierarchy in future.

Thanks again,

Steve.