Link: https://en.wikipedia.org/wiki/Domesday_Book

The Domesday Book is a land survey book from 1086, trying to record every shire in England.

The Anglo-Saxon Chronicle states that in 1085 the king sent his agents to survey every shire in England, to list his holdings and dues owed to him.

The survey's main purpose was to record the annual value of every piece of landed property to its lord, and the resources in land, labour force, and livestock from which the value derived.

The name "Domesday Book" [the Middle English spelling of "Doomsday Book"] came into use in the 12th century. Richard FitzNeal wrote in the Dialogus de Scaccario (c. 1179) that the book was so called because its decisions were unalterable, like those of the Last Judgment, and its sentence could not be quashed.

Basically King William rubbing his little hands and asking "How much money is coming my way?".