Levelling - Ordnance Survey's Levelling of Great Britain

Ordnance Survey's

Levelling of

Great Britain

This site is growing as a collection of information regarding the various levelling activities carried out by the Ordnance Survey since 1840. Levelling is the process of measuring the relative height marks across the landscape, and ultimately to a fixed datum - Mean Sea Level at Newlyn for the British mainland.

	England & Wales	Scotland	Link	Map
First primary levelling	1840-60		Abstract (Index) Transcription Project	Image
Second geodetic levelling	1912-21*	1936-52	Abstract (Companion) Transcription Project	Image Map
Re-levelling of Greater London	1931-34		Full Abstract Partial Abstract Transcription Project
Third geodetic levelling	1950-68	1956-68		Image Map
Cyclic relevelling	1956-89	1959-89
GPS era	1989-		GPS Website	Map

* Except parts of East Anglia and Kent, completed 1946-51

This website created by Barry Hunter as part of TrigTools. The 2GL Abstract has been scanned and compiled by Ian Richardson, as well as some browsing of the documents held at the National Archives. Transcription of the many pages of the 2GL abstract is been carried out by various volunteers. The 1GL abstract is has been scanned by Rod Sladen who has also helped immensely with this site and the 2GL Transcription.