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ArcGIS Network Analyst question:

I have a network dataset representing an archaeological site with ~500 buildings. Each doorway of these buildings represents a terminal node. I would like to simulate aggregate foot traffic patterns at the site.

One way to do this would be to generate least cost network paths from every node to every node. That is, generate 500 x 500 route matrix (250,000 routes). That is the same as doing a closest facility analysis for every building at the site. Of course, manually doing a closest facility analysis 500 times would be ridiculously time consuming.

Can I do it using ModelBuilder?

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The Origin-Destination Cost Matrix is the best workflow in Network Analyst for processing thousands of routes at once. It could easily generate a table with 250,000 rows describing the travel time between each unique pair of nodes. However, OD Cost matrix does not export the actual route geometry between each origin and destination, as stated in the Esri help page (emphasis mine):

The closest facility and OD cost matrix solvers perform very similar analyses; the main difference, however, is in the output and the computation speed. OD cost matrix generates results more quickly but cannot return the true shapes of routes or their driving directions. It is designed to quickly solve large M x N problems and, as a result, does not internally contain the information required to generate route shapes and driving directions.

Since you are interested in the location of foot traffic based on these routes (perhaps using the Line Density tool), I think you are stuck using the Closest Facility workflow. Fortunately, all Network Analyst workflows that can be initiated from the Network Analyst toolbar also have corresponding geoprocessing tools for use in ModelBuilder of Python:

  1. Make Closest Facility Layer geoprocessing tool. There are a cumbersome number of parameters required, but this is because there are so many options to tweak for Network Analyst workflows.

  2. Add Locations geoprocessing tool. This is just like using the "Add Locations" window from the table of contents.

  3. Solve geoprocessing tool. This is analogous to clicking "Solve" in the Network Analyst toolbar.

All toolbar items have geoprocessing tools

As is the case with all geoprocessing tools, you can drag and drop from the ArcToolbox pane (or the search pane) into a Model Builder model:

A basic model builder model

This model doesn't have an iterator, but it would be trivial to add one for rapid iteration through your routes. You would also need to add some tools to export your lines to individual feature classes somewhere on disk.

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