Visualize flows with FlowMapper

This article explains the presentation of flows on a map, using the FlowMapper plugin. For this demonstration, data on commuting patterns between 40 regions are used (from Statistics Netherlands).

Example of FlowMapper output (post-processed)

Example of FlowMapper output (post-processed)

Preparing the data

After the plugin is installed in the usual way, the manual can be found in the folder C:\Users\{username}\.qgis2\python\plugins\FlowMapper2_documentation.Three text files are required, with node coördinates, node names and a flow matrix. Three points must be stressed that are not mentioned in the manual. 1) The plugin does not work well with numbers with decimals. That can be solved by multiplying the numbers by (e.g.) 1000 and then round them. 2) As delimiters, both spaces and tabs may be used. The latter is especially useful when pasting data into a text file from Excel. 3) The node names should not contain spaces, because these are handled as delimiters. Replace them with underscores.

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Using QGIS processing scripts

One of the area’s that QGIS is constantly improving is the ‘Processing framework’, Formerly known as the sextante framework and written in java, it is rewritten in Python by one of the original authors Victor Olaya and made part of QGIS since about QGIS 2.0.

I think it is VERY usefull and in use a lot already, but not so much people are writing about this. In this blogpost I use it as a tool to run some pyqgis code, but Processing is much much more! Read about it in docs and manuals.

Recently there were some questions in the mailing list, which I thought would be fun to solve with a Processing script (instead of writing some lines of code in the python console, or creating a plugin).


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A QGIS class room setup on Windows

Somebody in my neighbourhood is Windows Administrator on a ‘Middelbare School’ here in Haarlem, my hometown.

The school, het Mendelcollege, received a (Q)GIS intro by Margit Stapel of GisWijzer who is doing introductions for 10 – 14 year old childer with GIS. The school received this course from a GIS professional as part of the ‘national geo week‘.


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Using MetaSearch plugin to search and load (meta)data from your National Georegister

We (mostly Tom Kralidis, Angelos Tzotsos with some additions by me) just released the MetaSearch Catalogue Client plugin for QGIS. The new plugin is an update of the CSWClient plugin from NextGIS. This new MetaSearch plugin makes searching metadata and using the services peanuts!

A Catalog Service for the Web (CSW), for example provided by the Dutch clearinghouse Nationaal Georegister, contains metadata about geographic data and services. The metadata not only provide descriptions, but can also contain hyperlinks to the services to directly view (e.g. WMS) or load (e.g. WFS and WCS) the geographic information.

Search and result based on several keywords in combination with a spatial constraint

Search and result based on several keywords in combination with a spatial constraint

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Generate series of maps with Python script

Sometimes you need to produce a series of similar thematic maps. The only difference is the field used to colour areas or show graduated symbols. Classifications or maximal symbol sizes are identical. For large numbers of maps it is quite annoying to repeat the same actions in QGIS over and over again. Moreover, mistakes are easily made this way. This article explains how the production of large numbers of maps can be automated with a Python script. All files needed to try this method are available in a ZIP file. This is a modified version of a previous article. This new method works better and faster than the previous one en works the same for Windows and Linux.

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Generate a series of maps 2 (Linux)

In a previous article I described how you can let QGIS generate a series of thematic maps with a batch file. This method was meant for the Windows version of QGIS. Now I have written a similar shell script for Linux (‘projectsnapshots’). You can find it in the ZIP file included with this article. It also contains all other files you need to test the script and an example of the result. The result consist of a series of images and a HTML showing all maps. The content could be copied and pasted in a word processing file. Before the script can be run, you have to make it executable. For further instructions I refer to the previous article. The script was tested with openSUSE 12.3. It works with QGIS 1.9.0-Master, but unfortunately not with QGIS 1.8.

Shell script to generate series of maps

Download ZIP file with shell script and sample files

Temporary Fix for OpenLayers Plugin

Current development version of QGIS ( upcoming QVIS 2.0 ) has undergone a nessecary upgrade of the Python-Cpp glue (SIP) which temporarily broke almost all python plugins. Currently plugin devs are busy fixing their plugins to be usable on time for the real launch of QGIS 2.0.

One plugin notably missing plugin is the OpenLayers-plugin, which is very usefull to use Openstreetmap (or Google or Bing) as a quick reference underground in QGIS. In the mailinglist the OpenLayers-plugin made it clear that there was currently no time available to fix this in a way they want it to be fixed (that is in a way that the plugin keeps working in both 1.8 and 2.0) and that there will be time to work on it during the QGIS hackfest in Brighton in september.

The good news is that the code of the plugins is available on Github. Because it was just easier to fix it only for QGIS 2.0 I did a quick fix to be able to use the plugin on my own build of QGIS (users of QGIS 1.8 should use the official version). The fixes you can find in my Github repo.

This fixed plugins is available for download here, but note that you can only use it by downloading it and unpacking it in the right plugin directory. On Linux this is ~/.qgis2/python/plugins and on Windows somewhere near C:\Documents and Settings\you\.qgis2\python\plugins. Note also that this is a temporary hack and that in time there will be an offical ( better :-) ) fix from the original authors.