What Makes a Map Good

The most useful maps distort what they depict and leave out tons of possible information

© Transport for London

From its earliest days, humankind has put thought into the world: cave art depicting animals, tallies on sticks and bones, and especially a wide variety of maps, suited to different purposes, from a small portable stone map found in Spain that was used for navigation by foot to the floating bamboo-and-shell “stick” maps that the Marshall Islanders used for navigating the open ocean. Different as they are, the best maps share core features. They aren’t always to scale. They mix perspectives. They depict as well as map. They omit masses of information. This isn’t just from ignorance or lack of technical sophistication—it’s by design. What’s included is exactly the information that the map users need, uncluttered by information they don’t need.

Take, for instance, the London Tube map. Harry Beck’s map of the London Underground entered the world in 1931 and has since been imitated by transportation systems all around the globe. It shows — but distorts — a simplified skeleton of the train lines, depicted as lines running vertically, horizontally, or diagonally, by no means an accurate reflection of their pathways.

The insight that inspired the map came from electronic circuit diagrams, a fascinating instance of anachronistic analogical reasoning. Geography doesn’t matter for electricity. What matters are paths and connections, gateways to other paths. The same for commuters, Beck reasoned. What commuters needed were the paths from station to station and the connections to other Tube lines, not geographic accuracy.

His design met resistance from the powers that be but was an instant hit with commuters. It’s so legible. The Tube lines are color-coded. The horizontal, vertical, or diagonal lines are easy for the eye to follow. The stops are indicated by name and perpendicular blips, and the connections to other Tube lines are clearly marked by circles.

The Tube map includes only a small fraction of the possible information, and what it includes is exactly what users typically need: paths and points where actions can be taken—specifically, switching Tube lines, entering, or exiting. It distorts distances and directions.