Buying and selling land became more frequent in late Tudor times and gave employment to the first professional surveyors, their work made possible by new means of measurement and calculation.
William Senior, who described himself as a 'Professor of Arithmetique, Geometrie, Astronomie, Navigation, Dialling and the makinge of all mathematicall instrumentes', came from Hull to Derbyshire at the invitation of the 1st Earl of Devonshire in the autumn of 1609. Senior's survey establishes the precise details of the lands owned by Bess of Hardwick's sons Henry (died 1616), William (created Earl of Devonshire 1618 and inheritor of Chatsworth) and Charles Cavendish and their sons. It was intended to give a comprehensive picture of the inheritance and enable the estates to be more efficiently managed. The work began in 1609, the year after Bess' death, and went on intermittently for 31 years. The atlas of 68 maps and associated survey records boundaries, field names, tenants, and (occasionally) land use. Senior's maps are extraordinary in their detail and accuracy.