The Century Slider
One hundred and fifty years of African population on one map. Drag the year from 1950 to 2100, or press play, and the fifty-four countries resize; switch the scaling from everybody to the working-age population aged 15 to 64 and the map redraws around the people who actually produce the output. Hover a country for its population, its working-age share and its share of the continent in that year; the panel also carries Africa’s share of world population, which is the number Chapter 1 opens on.
The two views are the argument. Term one of the book’s identity is working-age population growth, not population growth. A country 40 per cent of whose people are under 15 has far fewer workers than its total suggests, so the countries still early in their fertility transition are much smaller circles under the working-age view than under the total view. The gap between the two maps in any given year is the part of the demographic dividend that has not arrived yet, and the speed at which it closes is a fertility question before it is an economic one.
The confidence layer is the same flag the cards carry. It fades every country whose card confidence flag is low or cannot be computed at all, and it is the same flag the Growth Pole Map and the country cards show, read from the same record, so the three cannot disagree. Fading thirty circles is not a disclaimer at the bottom of the page: it is the map saying which parts of the pattern you are reading are an artefact of who runs censuses.
A projection is not a measurement. Everything after 2024 is the UN medium variant, one path through a fan of them. The slider reads that variant’s arithmetic; it does not promise it.
Open the slider in its own tab, worth doing on a small screen, where the whole viewport goes to the map instead of a frame inside a page.
Start at 1950 with the total-population view and press play. Africa is a continent of small circles, in a world it was then about nine per cent of. Stop at 2024, then at 2050, then at 2100, and watch which circles do the growing: the increase is concentrated in a handful of countries that are not, on the whole, today’s largest economies.
Now switch to the working-age view and run the century again. The same countries are still growing, but their circles in the early years are much smaller relative to the total view, because so much of their population is under 15. That is the dividend arriving late, and it is the difference between a population projection and a labour-force projection.
Then turn on the confidence layer and run it a third time.
- Which of the eight countries whose population at least doubles between 2024 and 2054 still looks large under the working-age view in 2050?
- Which of them survive the confidence layer as well, and which fade?
- Africa’s share of world population is in the panel in every year. At what point in the century does the working-age share of the world catch up with the total share, and what would have to be true about fertility for that gap to close sooner?
The page draws the UN World Population Prospects 2024 medium variant on a grid of every fifth year from 1950 to 2100 plus 2024, and takes the confidence flag from the country cards. Circle area, not radius, is proportional to population. A year the source does not publish draws no circle and is named in the panel; it is never a zero. The country outlines are Natural Earth’s 1:50m admin-0 boundaries, public domain. Morocco–Western Sahara is hatched and has no circle; Somaliland is dissolved into Somalia, because the book gives it no card and a border on a map is a claim. The vintage of every series the book quotes is listed on the About the data page.
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