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When Graphs Are a Matter of Life and Death

The New Yorker: “…In A History of Data Visualization and Graphic Communication (Harvard), Michael Friendly and Howard Wainer, a psychologist and a statistician, argue that visual thinking, by revealing what would otherwise remain invisible, has had a profound effect on the way we approach problems. The book begins with what might be the first statistical graph in history, devised by the Dutch cartographer Michael Florent van Langren in the sixteen-twenties. This was well into the Age of Discovery, and Europeans were concerned with the measurement of time, distance, and location. Such measurements were particularly important at sea, where accurate navigation presented a considerable challenge. Mariners had to rely on error-prone charts and faulty compasses; they made celestial observations while standing on the decks of rocking boats, and—if all else failed—threw rope overboard in an attempt to work out how far from the seabed they were. If establishing a north-south position was notoriously difficult, the spin of the Earth made it nearly impossible to accurately calculate a ship’s east-west position…The originality of van Langren’s graph attests to a long history of missed opportunities to arrive at the same idea. Friendly and Wainer offer an example from the banks of the Nile, which, before the Aswan Dam was built, in the nineteen-sixties, flooded each year. “Egyptians, who knew that their prosperity depended on the river’s annual overflow, had been keeping the Nile’s high-water mark for more than three millennia,” they write. The records helped farmers track the level of flooding in the recent past and decide when and where to plant crops. But, over thousands of years, nobody realized the significance of the data in aggregate—until the nineteen-fifties, when William Popper used it to chart the Nile’s flood levels in the course of thirteen centuries. Friendly and Wainer write, “No one thought to make a graph of the high-water level over time or compare the average water level in the last decade to what might occur in the next.” Popper’s work showed, for the first time, the surprisingly wide variation in silting across different periods—and silting was an important factor in fertilizing crops. Fat years and lean years didn’t just happen…”

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