A Brief History of the World in 47 Borders summary

Picture yourself on a beach at dusk, a few coconut cocktails deep, squinting at the lush green islands on the horizon. You and your friend, sitting next to you, strike a deal. Everything to the left of that jagged rock is yours forever, and everything to the right is mine. A third friend, who gets nothing but desperately wants your approval, agrees to witness it. Handshakes all around.

In the morning, you’d probably wake up mortified, realising you knew nothing about those islands, who lives there, or what the inhabitants might have to say about your arrangement. The crowns of Spain and Portugal felt no such shame.

In 1570, Gerardus Mercator published a map of Ireland so inaccurate that its northwestern corner sports what looks like a right angle. Then, eighty years later, came the Down Survey maps. These had coastlines in the right places, and Ireland looked recognizably the country you’d find in an atlas today.

The purpose of the new map was not academic. After crushing an Irish revolt, England’s 1652 Act of Settlement proposed repaying soldiers and creditors with confiscated Irish land. But first, the government had to know exactly what it was redistributing. So the surveyors mapped Ireland parcel by parcel, producing the first full-scale land survey of a nation.

In 1949, with the war that created Israel finally over, negotiators for Israel and Transjordan sat down with a map and a green pencil and drew the line between them. On paper, the mark was a millimeter or two wide. On the ground, that translated to 60 to 250 meters. Orchards, fields, and villages sat inside a line that was supposed to have no thickness at all. For twenty years, nobody could say for certain whether that territory lay in Israel or the West Bank.

The Green Line was provisional –⁠ armistice is a pause, after all, not a peace treaty. After Israel captured the West Bank and other territories in the Six Day War of 1967, the line effectively disappeared from Israeli maps.

In 2011, The Atlantic reported that the city of Detroit contained enough vacant land to swallow the entire city of San Francisco. Its main events stadium, the Pontiac Silverdome, had just sold for roughly what a modest one-bedroom apartment in Manhattan would cost. Some 50,000 stray dogs were said to roam the streets. Two years later, the city filed for bankruptcy.

This was a place that gave the world Ford, General Motors, Motown, and Eminem. What went wrong? Plenty –⁠ but one factor was a line on the map.

Stand on the brass strip marking the prime meridian outside the Royal Observatory in Greenwich and check your phone. It will tell you that, rather than being on the meridian, you’re actually about 102 meters inside the Western Hemisphere.

Today's prime meridian doesn’t actually run through the famous brass strip at Greenwich. Why? Because satellite measurements revealed that nineteenth-century astronomers had calculated their vertical slightly incorrectly. Rather than redo a century of measurements, scientists simply redefined the meridian. It wasn’t the first time. There is no natural zero point for longitude, so ancient geographers simply put it somewhere convenient. Eratosthenes, for example, just ran his through Alexandria, where he lived.