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I am using OD Cost Matrix layer in order to find distances between many origins and destinations points. It works fine, but I want to make sure the results make sense, and since OD Cost Matrix can only produce straight lines (and not true route shapes), I tried to calculate some specific origin-destination pairs using a Network Analyst regular Route layer and compare them to the OD Cost Matrix results.

However, in some of the cases the distances seem to be different between the two methods, even when I use the exact same analysis settings and network restrictions. Sometimes it's only a small gap, but in other cases it's probably a whole different route.

Shouldn't the two tools produce the exact same routes?

  • Which version of ArcGIS do you use? Is there a hierarchy attribute in your network data? – GISGe Feb 26 '15 at 15:24
  • ArcGIS 10.1 (Basic). There is a hierarchy attribute in the network data. – isshp Feb 26 '15 at 15:27
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    There are bugs related to OD cost matrix calculations. Depending on the number and location of origins, the results can be totally different. If the size of your data allows it, you could try to run a Closest facility analysis instead, it uses a different algorithm and you could check the shape of the resulting route. There are also bugs related to hierarchy and restrictions, but they are said to be solved in 10.0. – GISGe Feb 26 '15 at 15:48
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So here are the code and summary of the aforementioned bugs, as requested by @Chris W. Basically they seem to refer to the same issue and to have the same cause, i.e. a problem with the OD cost algorithm.

  • NIM094092 - The OD cost matrix analysis in ArcMap returns different travel time results for one origin if another origin is present.
  • NIM060948 - Time and length returned from solving OD Cost Matrix problem varies between the same origin and destination depending on the number and location of input origin points.
  • BUG-000084762 - When solving an OD Cost Matrix for a large network dataset using Hierarchy, erroneous results are returned in a small number of combinations where the route connecting an Origin and a Destination is of a longer duration than any other route from the same Origin and Destination that diverts through a third location.

They've been found between versions 10.0 and 10.2.2 and are all assigned.

As I commented before, an alternative could be to use Closest facility analysis (in an automated process) to get a similar output and see if the results are more reliable. I suppose the feasibility of this depends largely of the number of origin and destination points.

  • Thank you for your answer. So basically you can never trust OD cost matrix output? That's quite disturbing, I use this tool a lot. – isshp Mar 1 '15 at 8:31
  • @israel1986 I wouldn't go so far as to say that, I've used OD cost matrix and never noticed odd results - didn't double check every single result though, but the global range of values looked normal. Bugs are not always experienced by all users - otherwise Esri would probably put more effort in fixing them quickly. – GISGe Mar 3 '15 at 7:12

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