OSBM Ordnance Survey's
Levelling
of Great Britain		 [2GL Abstract]
[2GL Transcription]		 TrigTools


This page hasnt been updated since 29/9/04!!!!!

Recommend you visit the Whats New for November '04 or Links & Sources.

See the TIMELINE England
& Wales		 Scotland
First Primary Levelling 1840-60 1840-60
Once we have had a change to study the abstract there will be more about this levelling.
Data Sources
  • Map included in the 2GL abstract ( Map )
  • Abstracts of the principal lines of spirit levelling in England and Wales / by Henry James. (1861)
  • ( Index ) - More to Follow
Second Geodetic Levelling 1912-21* 1936-52
This was when the first Flush Brackets where used, because these have a unique number on, this is what started many peoples interest in them. (but they where first 'found' and studied on Trig Pillars)
Data Sources
  • Primary Lines In Process of Been Transcribed ( Progress - Abstracts )
    • From: ABSTRACTS of the PRIMARY LINES of the SECOND GEODETIC LEVELLING in ENGLAND & WALES by Colonel Sir Charles Close, KBE, CB, CMG, FRS Director-General of the Ordnance Survey Southampton 1921
  • Have diagram showing lines and approx. locations of Primary Lines and FBM's
  • National Archives at Kew seem to hold records for all the lines and Areas. ( Index )
  • other Levelling Files held at National Archives, Kew
      ( Index ) ( Glass Lantern Slides )
Results
  • Primary Lines of England and Wales ( Data - Map )
  • All Fundamental Benchmarks have been identified ( List - Map )
  • To be incorporated into a new site (still under-development)
Third Geodetic Levelling 1950-68 1956-68
Little definitive data has been found, what is known about this is largely guesswork and from references in many books.
Data Sources
  • Diagram of the Primary Levelling Lines ( Files section of Trigonomy Yahoo Group )
  • Many people have apparently stumbled upon many of the FB's used in this period, photos of many are found on OSBM msn Group, newly installed ones will largely have the G prefix.
  • other Levelling Files held at National Archives, Kew
      ( Index ) ( Glass Lantern Slides )
Results
  • Fundamental Benchmarks ( List - Map )
  • To be incorporated into a new site (still under-development)
Cyclic relevelling 1956- 1959
More to Follow - no definitive data has been found, but likely that a number of the benchmarks used are included in OSBM msn Group
 
the GPS era  
Around 1989, OS abandoned the Levelling Networks and replaced them with GPS based solutions. Many of the Fundamental Benchmarks (FBM's) where in fact reused as Passive Stations, which are the new markers that are in fact used for Height and Position.
Data Sources
Results
  • This is still been correlated how it all fits with the Levelling networks and

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