While spending the Christmas time of 1085 in Gloucester, William had deep speech with his counsellors and sent men all over England to each shire to find out what or how much each landholder had in land and livestock, and what it was worth.
Source: Wikipedia

Many incidental aims have been highlighted - the settlement of disputes, confirmation of legal title, a line drawn under the Conquest - but most historians agree that the principle concern of Domesday Book was royal revenue, and its main purpose was to increase it.
Source: http://www.domesdaybook.net/helpfiles/hs520.htm

Oh how much we've learned in the last 1,000 years.