I'm using the Network Analyst extension in ArcMap 10.2 to calculate the shortest routes between ~50000 pairs of stops. As the impedance is set to "Length (Meters)" the resulting Routes Featureclass has a field for "Total_Length" and "Shape_Length". What is confusing me, is that the values in these two fields are not the same, they differ by +15m to -0.5m. At first I assumed that this had something to do with the distance of the stops to the network, but looking more closely at some of the routes, the distance to the network doesn't match the difference in length. I've also re-run my analysis with a 0m offset of the Stops from the network, but the length differences stayed the same.

Has anybody else come across this before or does anybody have an idea of why this is happening?

  • Here, I have same problem as well. Did you find an answer? – user30623 May 26 '14 at 15:21
  • Is there any chance you are performing your measurements in a geographic coordinate system yet routing happens in the projected coordinate system? Make sure you use the same coordinate system when performing the measurements (and calculating the geometry length). Planar and geodesic measurements can give you a significant difference in some cases. Add a simple ~100m route between two points and play around with coordinate system (GCS_WGS_1984 and WGS_1984_Web_Mercator_Auxiliary_Sphere would work fine) when measuring the distance of the output route feature. – Alex Tereshenkov May 26 '14 at 16:28
  • Yes, I checked the coordinate system and they were the same for the network and for all my maps. – user28719 May 27 '14 at 14:57

Correct me if I'm wrong,

If you used Closest facility, that kind of error corresponds to the distance needed to get to the closest part of the road (SnapX, SnapY)

If you used OD Matrix, that distance is the difference between the distance on the road network and the distance on the a straight line.

I always use Total_Length.

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  • The error remained even when I set the snapping distance to 0. – user28719 Jan 8 '16 at 15:03
  • As I understand it, snapping distance doesn't have anything to do with it. The Shape_Length is the length of the line you see created. It has nothing to do with Network analyst, you see that for every line. The Total_Length is the distance the Network Analyst thinks is needed to get from Point A to Point B. That is the length of the road network you use, plus anything you walk to get on the road. – pankgeorg Jan 9 '16 at 17:27

Total_Length seems to be the (more realistic) 3D length of the route, Shape_Length the planar length. I did the following test: Exporting the route - which has a Polyline ZM Geometry and calculated the 3D Length - In my case (starting and end poins directly on the line segment) the 3D length equals the Total_Length.

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