[pgrouting-users] PgRouting and sub-networks / catchments

Peter Schmiedeskamp peter at thoughtspot.net
Wed May 25 13:18:21 EDT 2011

Dear PgRouting list,

I posted this question to the gis.stackexchange.com site a few days
ago, but haven't had any responses. I'm reposting here in hopes that
someone on this list may be able to help.

I have a polyline shapefile representing a road network and a second
shapefile containing points. I would like to use PostGIS (presumably
PgRouting) to identify sub-networks or service areas radiating from
these points.

Essentially, I am hoping to ask the question, "Starting from point X,
how far could I walk in any given direction, given a total travel
budget of 1 km, following the road network?" The result would be a set
of clipped polylines representing the total range of travel
possibility, given a 1 km travel budget.

For reference, this GRASS analysis appears to be exactly what I want
to do (except I want to do this in PostGIS):

This next example appears to be almost what I want to do, except it
seems to answer the question "which nodes could I travel to given a
travel budget of X distance?"

The second is not quite the answer I'm looking for, as I want the
polylines clipped to my travel distance--I don't care if I make it all
the way to a node.


P.S. If anyone is interested in why this sort of analysis is useful,
this journal article (hurray for open access journals!) explains how
network buffers are more appropriate for some urban transportation
planning applications. When you're dealing with pedestrians in areas
with large superblocks, this also helps explain why distances to nodes
are not quite accurate enough.

Oliver, Lisa N, Nadine Schuurman, and Alexander W Hall. 2007.
Comparing circular and network buffers to examine the influence of
land use on walking for leisure and errands. International journal of
health geographics 6, no. 1 (January): 41. doi:10.1186/1476-072X-6-41.

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