First Scottish QGIS user group

Together with the good folks at thinkWhere I have been organising the first Scottish QGIs user group meeting.  It is happening on 19th March 2014 in Stirling at the Stirling Management Centre.  Doors open at 9:30 with a 10:00 start.  Registration is through Evenbrite ( and there are 50 places available working on a first come, first served basis.

Details on how to get to the Centre are available here (

The agenda will be published a bit closer to the time once speakers have been finalised.  If you would like to present let me know as it would be good to have a mix of input to the day.  There are both 20 minute and “lightning talk” 5-10 minute slots available.

A big thanks to thinkWhere for hosting this first QGIS event in Scotland and QGISUK for enthusiasm and passion.

PostGIS Spiders

I had a request for some “spider diagrams” showing the connections between service centres and their customers and was given some sample data of about 140000 records.

QGIS spider/hub diagram

The data contained a customer ID and customer coordinates and a service centre ID.  Using another table of service centres I was able to add and update for each record the service centre coordinates (eastings and northings on the British National Grid EPSG:27700). Continue reading PostGIS Spiders

Speeding up pgRouting

pgRouting and accessibility
pgRouting and accessibility

I have been using pgRouting for some accessibility analysis to various facilities on the network and experimenting with different ways of making the process faster.

My initial network had 28000 edges and to solve a catchment area problem for one location on the network to all other nodes on the network was taking 40 minutes on a 2.93GHz quad core processor with 4GB RAM (Windows 7 PostgreSQL 9.2 PostGIS 2.0.3 and pgRouting 1.0.7).  I put the query into a looping function that processed the facilities in order but any more than 4 and the machine would run out of memory as the complete solution is stored in RAM until the loop finishes.

First step, reduce the number of edges in the network to 23000 and number of nodes to 17000 by removing pedestrian walkways, alleys, private and restricted roads.  Now the query is solved in about 12-14 minutes using about 200MB RAM per facility. Continue reading Speeding up pgRouting

Open-source GIS cluster

This is the challenge for this week.

PostgreSQL + PostGIS + MapServer + MapProxy + Quantum GIS on Windows 7 32-bit

The aim is to create a scalable mapping solution based on open-source software that is easy to use and maintain, is fast and responsive and that can provide data in a number of different formats. Windows installers are available for most of the applications I wanted to use which made life a bit easier. Doing the same thing on Linux might be even easier. The corporate proxy and firewall certainly made things more complicated than they should have been.

mapserver + mapproxy + client Continue reading Open-source GIS cluster