Demand Point Behaviour during Location-Allocation

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11-07-2019 12:56 AM
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New Contributor II

Hello,

I am running Maximum Capacitated Coverage Location-Allocation with about 6000 demand points and 8 facilities. I was wondering about the demand point's behaviour during this analysis. 

1. If the demand point is not located directly on a network, does it search for the nearest (Euclidian Distance) network, go to that chosen network by straight path, and then follows the Dijkstra's algorithm to the closest facility? 

OR

2. Does it head in the straight direction of the closest facility (Euclidian distance) until it reaches a network, and then follows the Dijkstra's Algorithm to the facility?

I would love if there are any sources related to this topic as well. 

Thank you in advance.

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Esri Contributor

It would be 25 minutes purely travelling on the road. NA can only accrue costs when travelling on the network, since it reads the edges. If a point is not on the network, it can't travel any edges to get from the network to that point, so no cost accrued.

-Rachel

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Esri Contributor

Hi Joseph,

It seems like there's 2 main questions here, so I'll write them out below with answers.

1) How does network analysis deal with inputs which are not directly located on a network edge/junction?

When loading inputs into a network analysis layer, network analysis objects are created for each input. The network analysis object has it's own network location, which is it's position on the network. If the object isn't directly on a network feature, then the analysis layer will do a search to find the closest network feature and kind of snap to the feature. The proportional location of the point on the line becomes the network location. Check out What are network analysis objects?—Help | ArcGIS Desktop  for more information on network analysis objects and network locations.

2) Is the Location-Allocation analysis using Dijkstra's algorithm?

The LA solver uses an OD Cost Matrix as part of it's calculation, and the OD Cost Matrix uses an algorithm which is based on Dijkstra's. You can read more about the algorithms used in network analysis here Algorithms used by the ArcGIS Network Analyst extension—ArcGIS Pro | ArcGIS Desktop 

I hope this answers your questions!

-Rachel

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New Contributor II

Hi Rachel,

Thanks for the reply! 

So when the network analysis object snaps to the closest network based on the search tolerance, does it include that distance/time (between the object and network) in the network analysis solution? Say if my impedance cutoff was 25 minutes, is that purely 25 minutes of traveling on road, or does that also include the time to get to the network? 

Thanks,

Joe

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Esri Contributor

It would be 25 minutes purely travelling on the road. NA can only accrue costs when travelling on the network, since it reads the edges. If a point is not on the network, it can't travel any edges to get from the network to that point, so no cost accrued.

-Rachel

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New Contributor II

Thanks, this answer my question! Have a great day.

-Joe

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