I'm trying to create a map with isolines for the road-distance places are from bus routes. I was trying to roughly follow http://jcastellssala.wordpress.com/2012/05/07/basic-network-analysis-with-grass/ but I don't quite get similar results (I feel like the network isn't completely connected, but this is the first time I'm doing this so it's more likely I'm just doing it wrong.
I am using the following shapefiles in SRID 2272 (NAD83 / Pennsylvania South (ftUS)): http://jimkeener.com/grass-topo-question/roads.tar.bz2 which is the TIGER road graph for Allegheny County, PA, USA (state fips = 42, county fips = 003), but reprojected to 2272 and a "length" attribute added. http://jimkeener.com/grass-topo-question/stops.tar.bz2 which is derived from the Port Authority of Allegheny County GTFS file found at http://www.portauthority.org/paac/CompanyInfoProjects/DeveloperResources.aspx and reprojected to 2272. So, the first thing I did is import these files: > v.in.ogr dsn=roads.shp layer=roads output=roads > v.in.ogr dsn=stops.shp layer=stops output=stops (http://jimkeener.com/grass-topo-question/ac.png) Then I connect the stops to the network > v.net input=roads points=stops output=network operation=connect thresh=500 Connect the require database layer > v.db.connect map=network table=schools layer=2 Then allocate the network > v.net.alloc --overwrite --verbose input=network output=network_alloc > ccats=1-6965 (http://jimkeener.com/grass-topo-question/ac-alloc-zoom-thumb.png when displayed with d.vect -c) (the little Xs are bus stops And create isolines at 1-, 2-, and 3- thousand feet > v.net.iso --overwrite input=network output=network_isolines ccats=1-6965 > costs=1000,2000,3000 afcolumn=LENGTH abcolumn=LENGTH (http://jimkeener.com/grass-topo-question/ac-isolines-zoom.png also with d.vect -c) All but a few of the roadways near the open space to the right (a park and very hilly (even by Pittsburgh standards:-p) area) are within 3000 feet of a bus stop. Therefor I was expecting almost all of the roads to be highlighted in different colors representing their distance from a stop. Thank you for any help! Jim
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