Down Survey

The Down Survey was a cadastral survey of Ireland carried out by William Petty, English scientist in 1655 and 1656.

The survey was apparently called the "Down Survey" by Petty because the results were set down in maps; 'admeasurement down' was used; it is referred to by that name in Petty's will.

In August 1649 the New Model Army, led by Oliver Cromwell, went to Ireland to re-occupy the country following the Irish Rebellion of 1641. This Cromwellian conquest was largely complete by 1652. This army was raised and supported by money advanced by private individuals, subscribed on the security of 2,500,000 acres (10,000 km²) of Irish land to be confiscated at the close of the rebellion. This approach had been provided for by the 1642 Adventurers Act of the Long Parliament, which said that the Parliament's creditors could reclaim their debts by receiving confiscated land in Ireland.

The Act for the Settlement of Ireland 1652 provided for the confiscation and re-distribution of the lands of the defeated Irish, mostly Confederate Catholics, who had opposed Cromwell and supported the royalists. Parliamentarian soldiers who served in Ireland were entitled to an allotment of confiscated land there, in lieu of their wages, which the Parliament was unable to pay in full. Lands were also to be provided to a third group, settlers from England and America. The dispossessed landholders were to be transported to Connacht and to other countries.

To facilitate the re-distribution, an accurate survey of the lands was required. Benjamin Worsley, the Surveyor General, had made a survey in 1653, which was notoriously erroneous. The Civil Survey which preceded the Down Survey was not a mapped survey, but provided detailed descriptions of boundaries and valuations of holdings, and its data was used as input to Petty's survey. William Petty, then physician-general to the Irish armies, on a leave of absence from his position as Professor of Anatomy at Brasenose College, Oxford, pointed out the defects and suggested remedies. He offered to undertake a new survey which would be concluded quickly – within thirteen months, more cheaply than the surveyor-general's proposals, and he would prepare a general map of the country. Despite Worsley's objections, the contract with Petty was signed on 24 December 1654.

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