The Map Is Not the Territory

The drawing puts two maps side by side: a diagram that gets you across London, and a chart that gets a ship across an ocean. Both are wrong about distance on purpose, so they can be right about something else.

Before you start. You don’t need geometry or economics for the first half. If you’ve ever used a subway map, or watched a number everyone was told to hit stop meaning anything the moment people started chasing it, you already have both examples this lesson runs on.

The idea in 30 seconds

A map earns its use by being honest about one relationship (order, on the Tube) and openly silent about the rest (distance) - that choice is an abstraction.
No flat map of a round Earth can be honest about both shape and area at once. It’s provable, not sloppy cartography.
Fixing one kind of wrongness on a map doesn’t remove it, it moves it to a different property, in the same amount.
A metric is a number you check in place of the thing you actually care about, because the real thing is hard to check directly.
Once people steer by a metric instead of just reading it, the metric can stop tracking the real thing. That’s Goodhart’s law.
A model - a map, a test score, a dashboard - works the same way every time: useful because of what it drops, dangerous the moment nobody remembers what that was.

Read the story · Skip to the numbers