Bet you've never noticed this about the Tube map

Why do some lines go over and some go under?

Much celebration today at the unveiling of a blue plaque to Harry Beck, inventor of the cultural icon and design classic that is the London Tube map. You don't need me to tell you about his genius insight that the map didn't have to be geographically accurate: that's in all today's news reports. (If you want to see a pre-Beck map, there's a fantastic original in a glass case outside Temple station.) Instead let me share my favourite little quirk about the map as it appears today.

Bet you've never noticed this about the Tube map

There are two sorts of Tube line: ‘cut and cover' (the early ones, like the Metropolitan and District, built by digging up the road, putting down the tracks then relaying the road), and ‘deep level' (made by tunnelling much further underground, for instance the Piccadilly, Northern and Central lines).

Take a look at the Tube map: whenever a cut and cover line crosses a deep level one, it goes over rather than under it, to mimic what happens in reality. In the 1980s London Underground accidentally printed a version of the map where a deep level went over a cut and cover. Beautiful pedants that Londoners are, several wrote to point out the mistake. A new version of the map was duly issued.

Now that's what you call attention to detail. I bet old Harry Beck is smiling down in approval.


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Rubik's Cube

A Rubik’s cube has more combinations than light travels inches in a century. This is my favourite illustration of how a very small number of factors can produce an absurdly complicated situation. A silly little toy, with only three squares in each of its three dimensions. How can that get complicated? Well, as anyone who's ever tried to solve one just by guessing will tell you, it gets very complicated. The number of possible combinations is 43,252,003,274,489,856,000. Forget billions - that's 43 quintillion and change. (In fact the cube's manufacturers just said ‘billions' in their advertising, figuring that no one would know what a quintillion was. It's a billion billion.) The number of inches light travels in a century, meanwhile, is a mere 37,165,049,856,000,000,000. Or thereabouts.