isobase

noun

1. A line drawn on a map or chart connecting places of equal or constant land upheaval or subsidence.

   “Assuming their zero isobase and assuming also that they have correctly identified the beaches, the Jamieson hypothesis is decidedly not favored by their field observations.”

   “The southern limit of Wright's zero isobase should intersect the north-west coast of England 125 km further north in the vicinity of the southern shore of Morecambe Bay.”

   “The isobase map shows the marked spatial variability in elevation of archaeological sites from the Groswater Bay west along Lake Melville to the Goose Bay area, as identified by Fitzhugh (1972).”