(or “the incredible shrinking treemap” HT @albertocairo).
Treemaps are a really useful way to understand hierarchical data, but they are not well-suited to side by side comparison.
Recently I’ve been working on the World Bank’s Atlas of the Sustainable Development Goals 2017 (which was a large team effort). One highlight that I worked on was a comparative treemap / cartogram of people living in extreme poverty, which is a bit different from the typical treemap.
Here’s one version, an animated GIF that Tariq Khokhar captured (you can see the interactive timeline here):
I believe strongly in simple models and straightforward measures. But even the simplest measures can hide complexity and strong assumptions. This was brought home to me by two stories that have been in the news in the last fortnight, relating to two of the most common numbers you will come across in social science research and reporting: the unemployment rate and life expectancy. Both news stories raised questions about how these numbers were interpreted.
This is the first of what may become a series of posts, and focuses on life expectancy.
Trending #8 on BBC News recently was “How in a single year did life expectancy in the US drop by 12 years?”, a clickbait title for a story about the Spanish flu of 1918, which swept across the world in the wake of the First World War.
The 12 year drop caught my attention, so I dug around, and – confusingly – this statistic is both true and highly misleading. Like the “interest rate”, there is no single thing called “life expectancy”. Media reports rarely explain which version of life expectancy they mean – in this case the BBC links to a US National Archives webpage which is no more specific, and doesn’t cite a source. That’s frustrating, because there are important assumptions embedded in the ‘standard’ quoted life expectancy measure, which, spelt out, is ‘period life expectancy at birth’.
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Frequently Asked Questions
What am I looking at?
Every person counted in the 2011 census of England, Wales and Northern Ireland is represented as a dot on this map – all 57,886,775 of them. Each dot’s location is near to a person’s usual residence, but the locations are not exact; public census results only report location to within a small area, usually containing a few hundred people. These are called ‘output areas’ in England and Wales, and ‘small areas’ in Northern Ireland. To create the map, I randomly place each person within their respective area. The colour of the dot reflects the person’s ethnicity as reported on the census.
Can I use this map?
Yes, with attribution. Consider it CC BY 3.0 licensed. The data is from the 2011 Census, via ONS (England & Wales) and NISRA (Northern Ireland) and you should cite them too, as the original source of the data.