DORSET, England — On a late summer afternoon, I stand atop a cliff and look down at Durdle Door, a natural stone arch rising out of the Atlantic Ocean, carved by millions of years of wind and water.

The Wimborne St Giles estate map, which dates from 1659, was cleaned and restored by experts the the Dorset History Centre. The hand-drawn, colour map, owned by Lord Shaftesbury, shows field ...