A (not so good) example of a map

Visualization is a very powerful tool to share knowledge with people, when used properly. Last week there was some noise in the Belgian and French news and about a map of the Muslim population living in Belgium. The map was apparently first published in SudPresse, with a printed map to which I did not have access. A different, interactive map was also made by De Standaard in Flanders (the Dutch-speaking part of Belgium). There were many reactions to the publication of these maps, and I heard about it via this article on lemonde.fr.

First of all, there seem to be many flaws in the research that led to the publication of this news, which has apparently been criticized by other sociologists in Belgium. This is the most important problem here : if the data is of dubious origin or of poor quality, your visualization will necessarily be wrong and misleading.

The interactive map that was made based this research also has a few important problems in my opinion :

  • The color scale uses a linear color gradient (from grey to dark green) to display non-linear intervals : from 0 to 1 %, 1 to 2 %, 2 to 5 %, 5 to 10 %, 10 to 20 %. This results in a map where the majority of the country is colored, even though the Muslim population seems to concentrate in a few areas (Brussels, Antwerp, Ghent, for instance).
  • But for the colored areas, the map is empty. There are no cities displayed on the map. The result is once again an impression that Muslims are everywhere in Belgium, with some blur areas where their proportion is higher. I’m assuming that there must be quite a bit more to the data than this !
  • The source of the data isn’t very clear. The Pew Research Center and the German Federal Office for Migration and Refugees are mentioned, but it is not clear what data was actually used. Was it related to this report for instance ? I have no clue, and I am unable to check the features in the data myself.
Screen capture of the map on De Standaard's website.
Screen capture of the map on De Standaard’s website.

The resulting map in my opinion is unclear enough to be used by anybody, including for xenophobic purposes, even though that doesn’t seem to have been the goal of the author. I believe that any author of visualizations bears a responsibility towards her readers and towards the people who produced the data. This is especially true about such sensitive topics as Islam and immigration in Europe nowadays.

If you want to read more about the dangers of visualizing data without properly understanding or checking it, I recommend “Unknown unknowns”, a short article by Alberto Cairo about the dangers of “data ignorance”.

In case you didn’t know, constructive criticism of visualizations is a very popular sport in our domain. Take a look at Junk Charts or at this post by Alberto Cairo if you need to be convinced !

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