The chart gallery
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✎ Imagined · a drawing to show the idea A sketch in the style of the original 1786 · William Playfair
The line graph and the bar chart
In his Commercial and Political Atlas, Playfair drew England’s trade as two lines over time — money coming in and money going out. In the same book he drew a bar chart of Scotland’s trade with other countries, because he only had one year of numbers for it.
One thing to hold: Time runs left to right, and the gap between the two lines is the story: where they cross, the balance changed.
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✎ Imagined · a drawing to show the idea A sketch in the style of the original 1858 · Florence Nightingale
The rose (polar area) diagram
Nightingale nursed soldiers in the Crimean War. Afterwards she drew a wedge for each month, sized by how many soldiers died, and coloured by the cause. The biggest wedges were deaths from diseases that cleaner hospitals could prevent, not from wounds.
One thing to hold: A wedge’s AREA shows the count, so a wedge twice as long holds about four times as much. Read the area, not the length.
Be careful: Sizing by area makes big months look even bigger. It was built to persuade, and it did — but a plain bar chart of the same numbers is easier to compare.
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✎ Imagined · a drawing to show the idea A sketch in the style of the original 1854 · John Snow
The dot map
During a cholera outbreak in Soho, London, the doctor John Snow marked each death on a street map. The marks crowded around one water pump on Broad Street. He persuaded the local board to take the pump’s handle off.
One thing to hold: Where things happen can point to a suspect. A cluster on a map is a clue, not proof: Snow then checked who drank that water and who didn’t — the brewery workers nearby, who drank their own water, mostly stayed well.
Be careful: The outbreak was already fading when the handle came off, and the famous map was published the next year. The map helped convince people later; it did not stop the outbreak on its own.
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✎ Imagined · a drawing to show the idea A sketch in the style of the original 1900 · W. E. B. Du Bois and his students
Hand-drawn data portraits
For the 1900 world’s fair in Paris, the sociologist W. E. B. Du Bois and his students at Atlanta University hand-drew dozens of bright charts about the lives of Black Americans — where they lived, what they earned, the land they owned — to show progress made against injustice.
One thing to hold: A chart is made by someone, for a reason, for an audience. Du Bois chose bold colours and shapes so visitors would stop and look.
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✎ Imagined · a drawing to show the idea A modern sketch of the trend he found. His own figure was a table of counts 1886 · Francis Galton
The regression line
Galton set the heights of parents beside the heights of their grown children, in a table of how many families had each pair. Very tall parents tended to have children a little less tall, and very short parents children a little less short. The trend through the table pulled back toward the average — he called it regression.
One thing to hold: A trend line shows the pattern across many pairs, not a rule every pair follows. (Others had drawn scatter plots before him; the idea of regression was his.)
Be careful: Galton also invented the word eugenics and used statistics to argue for it — the false and harmful idea that some groups of people are better than others. The regression line is still useful; who uses a chart, and for what, always matters.
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✓ Seen · a record of the real thing Drawn from the published numbers 1973 · Francis Anscombe
Anscombe’s quartet
The statistician Francis Anscombe made four small datasets. They have almost the same averages, the same spread and the same line of best fit — but when you draw them, they look nothing alike.
One thing to hold: The same numbers can hide four different stories. Always draw your data before you trust a summary.