ordnance datum


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ordnance datum

n
(Surveying) mean sea level calculated from observation taken at Newlyn, Cornwall, and used as the official basis for height calculation on British maps. Abbreviation: OD
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5 hectares (ha) and has elevations of up to 150m above ordnance datum (AOD).
The benchmarks are used by land surveyors to record the height above Ordnance Datum (mean sea level).
3 metres above ordnance datum (the universal benchmark against which tides in Great Britain are measured).