Ordnance Datum
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Ordnance Datum
Vertical references in Europe

In the British Isles, an ordnance datum or OD is a vertical datum used by an ordnance survey as the basis for deriving altitudes on maps. A spot height may be expressed as AOD for "above ordnance datum". Usually mean sea level (MSL) is used for the datum. In particular:

Tunnel datum

Tunnel datum is a datum based on an ordnance datum and used in designing tunnels which pass below sea level.

  • for the London Underground, a tunnel datum of ODN -100 m is used;[2] thus a depth of -60 m AOD is 40 m ATD (above tunnel datum)
  • for the Channel Tunnel, a tunnel datum of ODN −200 m is used;[3] thus a depth of -60 m is 140 m ATD


  1. ^ a b Irish Grid Reference System Archived 2008-06-14 at the Wayback Machine from OSI website
  2. ^ "Victoria Station Upgrade Environmental Statement: Main Report" (PDF). Transport for London. 15 November 2007. pp. 2-6, §2.5.4, fn 2. Retrieved 2008.
  3. ^ Radcliffe, Eric (1995). "Control and Construction Surveys". In Colin J Kirkland (ed.). Engineering the Channel Tunnel. Taylor & Francis. p. 53. ISBN 0-419-17920-8.

External links

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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