calculating route diistance

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03-13-2012 02:50 PM
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Hi
I am trying to find out the shortest path between a point (which is projected to equal distance) and some school locations. I have built a network layer using Fairfax road and trying to load the locations as stops by using the load location tool. but whenever i try to solve it says "Stops" is on a non-traversable network element position".
I also tried the OD matrix to solve without showing the routes but it says the same. i don't understand where i did mistakes. my road layer has a restriction of 'oneway'. I also want to find out driving direction. I am really stuck and trying this for a week. What should i do now?
Any help is really appreciated.
Subrina
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Hi Subrina,

Have you tried turning off your one-way restriction on the route layer and re-solving? If you're able to solve with it off, it could be a problem with the one-way restriction evaluator. If you have other restriction attributes, also try turning them off.

Consider symbolizing restrictions on your network to get a better idea of what edges are blocked. See the section entitled "Symbolizing restrictions with arrows" of this help topic.

One other thing to try is the Network Identify tool on the Network Analyst toolbar. Use it to click on Fairfax Road to see the street's network attributes. In particular, see what the network cost is for the attribute you're solving on. If it's a -1 (or less), then this is causing your edge to be restricted.

Good luck, and please let me know how it goes.

Robert
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Hi Robert

Thank you so much. it worked 🙂 but still why can't i do measure the network distance when the restrictions are on??
I have one more q. i have 400 points from which i wanna know the distance of some hospitals. but these points are actually centroid of ZIP Codes which i created from the ZIP Code polygons. So, they are in different layers. That's why i have to take each centroid location at  a time and do the OD matrix. How can i take the centroid points in one layer so that i will have the network measure in one OD matrix attribute??

Thank you again
Subrina
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but still why can't i do measure the network distance when the restrictions are on??


Did you take a look at the evaluator logic in the one-way restriction attribute? Post it here so I can take a look too. Maybe the evaluator is restricting roads in both directions rather than in just one.

Aside from Network Identify and symbolizing restrictions, you could also try a service area analysis to see how far you can traverse on the network from your stops--just load the stops as facilities, set a reasonable break value, and see what the solver returns.

I have one more q. i have 400 points from which i wanna know the distance of some hospitals. but these points are actually centroid of ZIP Codes which i created from the ZIP Code polygons. So, they are in different layers. That's why i have to take each centroid location at a time and do the OD matrix. How can i take the centroid points in one layer so that i will have the network measure in one OD matrix attribute??


Sorry, but I guess I don't understand the question. Are you trying to figure out the nearest X number of hospitals, or how many hospitals are within X distance? Or do you have a set of hospitals and, for each zip code, you want to find the distance to a specific subset of those hospitals?

Thanks,
Robert
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Hi Robert

Sorry for late replying. I was sick. Actually i am thinking which one is the evaluator logic in the one-way restriction attribute? But i did the service area as you said and found that many of my centroid locations are on one way road. so i cannot find a service area away from that point. but my q is: if it is a one way there should be another road to the opposite direction. yet i understand ...it is the data layer which shows no alternative road to come back.
for hospitals, i have created the service area from centroids and can find out how many hospitals are located within certain distance from the centroid points along the network.
Thanks for your suggestions.

Subrina
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Hello Subrina,

Hope you're well. Judging from the graphic you posted, there is surely a problem with the Oneway restriction attribute. It is restricting your roads in both directions, rather than just one. Furthermore, it's restricting two-way roads--probably all of them. I say this because the road you identified in the graphic was a dead end and should be two-way--I've never heard of a one-way deadend before. 🙂

You'll need to correct the logic in your evaluator for the Oneway restriction attribute. The logic should look something like what's shown in the 5th and 6th graphics in the following help topic:
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Types_of_evaluators_used_by_a_network/...

You may want to go through the first Network Analyst tutorial exercise and pay particular attention to Step 24 when you choose Oneway. Also during that step, click the Properties button (on the right side of the dialog box) to get to the evaluator's logic.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Exercise_1_Creating_a_network_dataset/...

One other thing to consider is you can use the nationwide network dataset that comes with the Data & Maps DVD instead of making a network dataset yourself, and avoid some difficulties. But that's only if your study area is in North America or Europe.

Best,
Robert
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🙂
Thank you so much Robert

The deadend with one way was also new for me 😄

Thanks again
Subrina
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