Network Analyst results extending beyond the cutoff limit?

[Anonymous User]

I am working in Network Analyst to generate 1/2 mile walkshed buffers around specific origin points. The network includes a roads layer and a sidewalk layer. I set a cutoff limit of 2440 feet, however when I run the analysis, the results are extending out beyond 1/2 mile.

1/2 mile euclidean buffers are shown in red, and network analyst results are shown in orange. The orange points are the origin facilities from which the network is traveling away from. Does anyone know why the results are extending beyond the 1/2 mile buffer?

The corresponding results table is shown below and indicates that the maximum cumulative distance is 2440 feet, however this is not reflected in the results. All data is projected correctly and shape length fields appear to be calculating length correctly.

Thanks!

[MelindaMorang]

Assuming your cost attribute for distance is configured correctly, then most likely the facilities are being located on the network somewhere a little ways away from their geographic location.  When you run a network analysis, the input points have to "locate" on the network, meaning that they have to basically snap to the closest non-restricted network location.  That location is used as the start/end point for the network analysis.

Say the top point in your screenshot locates on a road to the north of its geographic position.  Then it's to be expected that the Service Area extends further north than you expected.  You can check the network location fields for each facility (SourceID, SourceOID, PosAlong, SideOfEdge), or if you re-load them with Add Locations, you can check on the Snap option to snap them to their actual network location.

[Anonymous User]

Hi, yes, I actually went through and added in lines to connect the facilities directly to the nearest sidewalk or roadway (shown in pink below) to try and mitigate this issue, and set my search tolerance to only 300 feet. Even so, the results are extending much more than 300 feet beyond where the anticipated 1/2 mile limit would be.

[MelindaMorang · Accepted solution]

Okay, then you probably need to check the configuration of your cost attributes and make sure they are calculating the distance correctly.

- Locate the network dataset in the Catalog pane

- Right-click it and open Properties

- Go to the Travel Attributes tab and the Costs sub-tab

- Find the cost attribute you've been using (the one your travel mode is using) and click on it.

- On the bottom half of the page, check the Evaluators section and make sure the calculations being used to calculate the distance are sensible.