My post yesterday discussed the mean centres of population of South Africa and its provinces. The mean centre is (relatively) easy to calculate, but it may not be the most useful type of population centre. It is essentially an arithmetic mean, which means that outliers can have a massive effect on the centre. It minimizes the average square of distance from the centre, not the average distance from the centre. The centre that does minimize the average distance is called the geometric median, and it is not quite so simple to calculate, since there is no closed form solution. But it can be done!

Follow-up: a subsequent post describes the geometric median centre of population, which is some respects a more sensible definition than the mean centre of population described here.

At some point in school, we South Africans are told that the official decimal separator is the comma.¹ Most of us then proceed to ignore this—at least in English use²—because it differs from the decimal point used in the rest of the English-speaking world, and thereby creates confusion. Thankfully, the maintainers of the glibc locale data—and thus the number formats used in Linux systems—agree with me on this question, and the South African English locale uses the decimal point.

Ever wondered where that (Western Cape registered) car is from? Wonder no more: (you can click on the map to see a bigger version)

I’ve drawn some maps showing the percentage-point change between the 2009 and 2014 elections in the vote share of the major parties (or, in the case of COPE, formerly major parties). Because municipal boundaries have changed a bit, I had to recalculate the 2009 results for the 2014 boundaries, by assigning the voting districts from 2009 to wards from 2014. In the cases where a 2009 VD was spread across multiple 2014 municipalities, I assigned it according to the location of the voting station.

The detailed 2014 election results map promised in my last post is live! It has all the features of the 2009 map, plus you can see the results from both the national and the provincial ballots. As before, you can zoom right down to street level and see the results for individual voting districts.

As a long-weekend project I’ve put together this interactive map of the 2009 South African election results. It’s a “slippy” (i.e. scrollable and zoomable) map and you can zoom right down to street level and see the results for individual voting districts. (Something you can’t do with the News24 election map!)

I have a new site up which graphically displays information about the results of the 2009 South African elections. This project was an exercise in learning to use the D3.js framework. All the code and data is available in a github repository.

New map I drew this weekend: it shows the spread of electrification in South Africa from 1996 to 2011, based on census data. The actual variable measured is “Main source of energy for lighting”. As usual, click for the full-size version.

I have added a layer showing the distribution of first/home languages from Census 2011 to my dot distribution map website. Next up: household income.