Datum Earth or the Datum is the only world in the Long Earth that humans evolved on. It was the only Earth most humans knew existed, before Step Day.[1]

The city Datum Madison was located on this Earth, as well as the world's version of the Yellowstone Supervolcano.[2]

Datum Earth is located in the middle of the Ice Belt, a band of cooler Earths.[3]

Worlds in the Long Earth are named after the amount of steps, either west or east, that need to be taken to reach it from Datum Earth. For example, 'Earth West 5' is located five steps West of the Datum.

The Long Earth

Many people left Datum Earth after Step Day, causing a decline in it's economy. One of the few boom elements was transport - Steppers can take you stepwise, but can't move you laterally at all. As a result, the Datum became the crossroads of the Long Earth.[4]

The Long War

This world's version of Yellowstone Supervolcano erupted in 2040. All the local versions of the volcano had been unstable, however this world was the only one that it happened on - scientists believed that this was because of the disturbances humanity had caused.[5]

The Long Mars

The Yellowstone eruption meant that the Datum become uninhabitable in many areas, and forced people to move into the Low Earths.[6]


The term 'Datum Earth' comes from the definition of the word 'datum': "a standard position or level that measurements are taken from".[7]



  1. The Long Earth - Chapter 2
  2. The Long War - Chapter 69
  3. The Long Earth - Chapter 18
  4. The Long Earth - Chapter 16
  5. The Long War - Chapter 69
  6. The Long Mars - Chapter 1
  7. "Datum", Wikipedia,
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