Cannot connect all origins to destinations using OD cost tool

Question

Dear all,

I have read about different posts on "OD cost matrix : Not all lines solved" but I still cannot figure out some issues in my case. I wanted to get lines from street nodes (blue dots as origin) to grocery stores (blue squares as destination) within individual service areas.  Although I checked and cleaned the street network to remove errors (dangles and pseudo nodes), I get only 1-2 lines that appear for each destination after solving the OD cost.  I wanted to get all nodes to connect to the grocery store within a particular service area.

I tried to play around with the settings changing the connectivity from "end-point" to "any vertex" and tried to re-run several times but still no good.Each time,  I get a message saying "Warning: No "Destinations" found for "Location 1" in "Origins".  I get a list for all of these locations.

I attached a sample of the issue I am having.  Can anyone help me out? I would really appreciate.

OD cost matrix issue.PNG

HollyTorpey_LSA_0-1777409792709.png

JaySandhu · Answer

You are using the right tool, OD Cost Matrix. But your network is not set up correctly to find the paths. Did you try the Service Area lines to see if your network is connected? How about the network identify?

One more thing to check: the locations you are using as your origins and destinations, are they included as a source in the network? If yes, then you need to remove them as a source. Generally you only need the line edges as a source in the network. If you add point locations as a source, they may be disconnected from the network and when you load the same points origins and destinations then they may not find any paths.

Jay Sandhu

YannickLi · Answer

Thank you for your kind response.  I tried the different options that you suggested.  However, after checking for connectivity, I still cannot resolve the problem of getting lines to connect the origins (street nodes) to the destinations (schools) using the OD cost tool.  Do you think that the school locations should absolutely be found on the road network itself? Do you have any other suggestions to help me out?

I would be open to use other tools to analyze walkability in the case that I cannot use the road network as input.  Anyone who could kindly contribute is also welcomed, thanks.

Yannick

JaySandhu · Answer

The number one reason for not finding paths to all the destinations is network connectivity or some restriction that is causing the network to be disconnected. You can check if the network is connected in a couple of ways:

1. Use the Network Identify tool. It is on the Network Analyst toolbar. Second icon from the right. Activate it and then click on a network edge. It will pop up a list of the attributes of that edge and the edges and junctions it is connected to. Is it returning what you expect? Are any restriction attributes set that will cause the edge to be not traversed?

2. Use the Service Area solver. Load one of your origins from OD as a facility. Bring up the properties of SA layer and on the Analysis settings tab set a break value of, say, 10 minutes (if using time). On the Polygon Generation tab, turn off the polygons. On the Line Generation tab, turn on the generate lines. Close the properties and solve the service area layer. This should draw all the lines connected to that origin within 10 minutes. Do you see what you think you should see Or is there disconnects in the network?

So if you do see disconnect, one potential thing to watch out for is the connectivity setting of the network dataset. Is this data supposed to connect at each edge end point OR is it supposed to connect to any vertices along an edge (yes if you got the data from a source like open streetmap). In that case you could switch the connectivity policy to Any vertex and rebuild the network. After a re-build of a network, make sure to, in the NA window, right-click the Origins and Destinations and recalculate location fields before you solve the layer again.

Jay Sandhu