topic Re: Route layer: different results with "same" network datasets in ArcGIS Network Analyst Questions

Route layer: different results with "same" network datasets

BarbaraSchneider1 — Fri, 14 Mar 2014 09:11:09 GMT

Hello,

I am using two network datasets:
1. street network dataset covering whole Switzerland
2. a clipped version of above covering only a part of Switzerland

With the two network datasets, I am calculation a route using the same input locations. The results are as follows:
1. With the street network covering whole Switzerland, there are unreached locations
2. With the clipped version everything is fine, there are no unreached locations

I don't understand why there are unreached locations in the larger network because the two street networks are exactly the same in the area of the route (= the clipped area)

Thanks a lot for your answers in advance

Re: Route layer: different results with "same" network datasets

RamB — Sun, 16 Mar 2014 05:08:31 GMT

Tolerance of location is usually an issue with changing scales. Are the input locations exactly same (same coordinates) ?

Re: Route layer: different results with "same" network datasets

BarbaraSchneider1 — Mon, 17 Mar 2014 08:45:27 GMT

Yes, the input locations are exactly the same.

Re: Route layer: different results with "same" network datasets

JaySandhu — Mon, 17 Mar 2014 22:33:35 GMT

Do you have hierarchy defined for your network? IF yes, is it being used? Perhaps the streets in the hierarchy are not connected in the full network causing the network search space to the different. You could try turning off the hierarchy to see if you will get the paths in the larger network. Also, are the restrictions set up the same way in both the network as they can also cause some locations not to be reached.

Jay Sandhu

Re: Route layer: different results with "same" network datasets

BarbaraSchneider1 — Tue, 18 Mar 2014 14:46:28 GMT

Hi Jay,

I am using hierarchy. I don't understand what you mean with the sentence:
"Perhaps the streets in the hierarchy are not connected in the full network causing the network search space to the different."

The streets in the hierarchy are connected both in the full network as well as in the clipped network. Is there a way I can define the network search space?

Thanks,
Barbara

Re: Route layer: different results with "same" network datasets

JaySandhu — Tue, 18 Mar 2014 19:56:35 GMT

First, Do you get the same route IF you turn of hierarchy of in the two network datasets?

If yes, then the hierarchy is playing a role in the differences.

Regarding my statement:
To find a path using hierarchy we are searching from both the start and end to get to the next level of the hierarchy and we assume that we can find a path using the hierarchy. But if the edges belonging to the hierarchy level are not well connected we do not find a path. So it is likely that if there are disconnected edges in the top level, a clipped portion of that may be connected.

SO let's first make sure that hierarchy is the reason why you are getting differences and then we can try to figure out a solution.

Jay Sandhu

Re: Route layer: different results with "same" network datasets

BarbaraSchneider1 — Fri, 28 Mar 2014 09:29:18 GMT

Hi Jay,

when I turn off the hierarchy for the entire network, there are no unreached locations.

Barbara

Re: Route layer: different results with "same" network datasets

JaySandhu — Fri, 28 Mar 2014 17:43:39 GMT

Barbara,

If hierarchy is off, you are able to reach everywhere. So this essentially boils down to the fact that there are disconnects in the streets that belong to higher level hierarchies.

Unfortunately there is no easy way to find the problem areas. One way is to select all the edges that belong to hierarchy 1 and export to a new feature class and then make a network on it and do a service area lines for a very large break value (turn off the polygons) and then examine the results to see if any lines are not part of the service area i.e., dis-connected. Then you would have to repeat this process by selecting hierarchy 1 and 2 and export them and check, etc.

Jay Sandhu

Re: Route layer: different results with "same" network datasets

BarbaraSchneider1 — Thu, 03 Apr 2014 13:02:53 GMT

Hi Jay,

thanks for your answer! I still don't understand why the streets are connected in the clipped network, but not in the full network. If it was the other way round (i.e. the streets in the clipped network are not connected because the connecting streets have been clipped off), I would understand it.

Barbara