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I'm new to GIS but thanks to the answers I got in another question here on GIS stack exchange I was able to increase my knowledge significantly. This question is related to an earlier question I asked and got answer, but since this is a new question, I thought better to ask a new question instead of continuing on the older one.

I have about 160,000 addresses (points) and a (vector format) map of roads and 10 city limits (polygon). I want to:

  • Calculate the distance from each of these addresses to the city borders (or possible the city centers - a point - if that is easier).
  • That is, for each city I want 10 distances. I don't just want the possibility to do it one by one - I want the total 1,600,000 distances once and for all!

I was earlier advised to use either Road Graph for QGIS og pgRouting for PostGIS. I have stated using Road Graph. I was able to import all the data into QGIS, install the Road Graph plugin, and calculate the distance between to points. My question now is:

  • How do I get Road Graph to calculate all the 1,600,000 distances? And can it at all be done with 'Road Graph'?

Thanks

  • distance as in a 'straight line' distance? – nickves Oct 9 '13 at 13:02
  • No, as in shortest path on roads. – Mace Oct 9 '13 at 14:05
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As far as I have understood Road Graph, it is very limited in its functionality. Only A-B routing on screen. No automation of processing.

  • Ok, thanks for the answer. Do you have another suggestion? Do you know if pgrouting can do this? – Mace Oct 9 '13 at 13:09
  • I would primarily suggest my own offerings from www.routeware.dk, but I guess pgrouting can also do it. – Uffe Kousgaard Oct 9 '13 at 13:27
  • Thanks - looking for a free solution though. – Mace Oct 9 '13 at 13:43
  • @Mace How big is your road graph (how many edges)? PgRouting should certainly be able to cope with 1-2 million routes without much fuss. – underdark Oct 9 '13 at 15:03
  • @underdark I have three levels of roads varying in size (freeway, interstate, and small road). I don't know exactly how many roads each one has. Preferably, I want to use all three types of roads, and then penalize using the small roads and the interstates, is this possible in pgrouting? I think pgrouting is the way to go for me no matter what, so I will try to get it working. – Mace Oct 11 '13 at 9:22
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I had to do something similar once upon a time, before pgrouting was mature. I wrote a simple PHP script that would query for the road graph and perform a Dijkstra search (PHP made for an easy "query container"). In my case, this worked because my graph was small. I also made things easier by eliminating nodes that didn't actually branch. Eg, if A->B->C, I just combined A, B, and C into one geometry.

TL;DR You're going to have to write a bit of software. Dijkstra implementations can be found easily, but you need to feed data into them yourself. If your graph is large, you're going to need to find a way to simplify.

  • Thanks for the input. I think I will look at pgRouting before starting to code myself. It already includes a Djikstra search as far as I know. – Mace Oct 9 '13 at 17:06

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