How the survey worked
- Fast. William Petty, an army doctor, signed the contract on 24 December 1654 and promised the job in thirteen months. The survey was accepted in May 1656.
- Soldiers, not surveyors. About a thousand men, mostly unemployed soldiers, measured with chains using simple instruments Petty designed. Draughtsmen in Dublin plotted their figures onto gridded paper.
- Profitable or not. Each parcel was marked as arable, meadow, pasture, wood, bog or mountain. Grants were reckoned in profitable acres, so bog and mountain often came along uncounted.
- Close, not exact. Checked against modern measurement, its acreages run on average just over 11.5% short.
- Huge. Petty counted 2,278 parishes. About 1,400 parish maps were drawn, each with a written terrier listing owners, religion and land use.