topic Re: Service Areas definition using Network Analyst in Public Transit Questions

Service Areas definition using Network Analyst

AlassaneBarro2 — Sun, 04 Oct 2015 14:43:42 GMT

I have a road network and a location from which I would like to define a 3-hour service area. I have followed a lab on how to proceed (from time calculation on each road segment, new network dataset creation, loading locations, and setting service area parameters), but I am still getting an unsatisfactory result. However, when I use the lab dataset everything works perfectly. Do you think topological errors in my road network, which I am 100% sure of the existence, is impacting my results?

Thanks

Re: Service Areas definition using Network Analyst

ChrisDonohue__GISP — Sun, 04 Oct 2015 15:58:38 GMT

Yes, I've found with Network Analyst that when things come out not-as-expected, it almost always is an issue caused by either lack of connectiveness or a Network-specific attribute being set wrong.

A quick way to check connectivity is to run another Service Area, but this time turn on the option to "Generate Lines". Once you have the output, you can visually look at the linework and see gaps.

As for finding and fixing connectivity, run Topology on the Linework. Be sure to specify rules.

Some Suggested rules:

Must Not Overlap
Must Not Intersect
Must Not Have Dangles
Must Not Self-Overlap

Note that you will likely have to do many Exceptions, as there are valid occasions for some of these. For example, some streets end as a cul-de-sac, so are valid yet will trigger a "Must Not Have Dangles" error.

Topology Rules

ArcGIS Desktop

As for Network-Specific Attributes, review your attributes to be sure that they are appropriate. Look for things like Oneway set in reverse of expected or a line segment being mis-set by a default attribute as non-traversable/prohibited.

ArcGIS Help 10.1

Give that a try. If you still run into trouble, post an image of what you got and a description of what you is going awry. Be sure to specify what version of ArcGIS you are using, as there have been some changes in the last few versions.

Good luck,

Chris Donohue, GISP

Re: Service Areas definition using Network Analyst

JoeBorgione — Mon, 05 Oct 2015 00:08:28 GMT

Chris' comments are spot on. Network analyses demand good data for good results. Clean things up and let us know if it improves your expected results.

Re: Service Areas definition using Network Analyst

AlassaneBarro2 — Mon, 05 Oct 2015 00:16:26 GMT

Thanks Chris. I will let you the results once I correct the topological errors.

Re: Service Areas definition using Network Analyst

AlassaneBarro2 — Mon, 05 Oct 2015 00:17:40 GMT

Thanks Joe. I will let you know once I clean up the data.