abstract: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".
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mean sea level calculated from observation taken at Newlyn, Cornwall, and used as the official basis for height calculation on British maps 法定基准线; 从对纽林、康沃尔观察计算出的平均海平面，用于英国地图的高度计算之官方依据 ( abbr: OD)