an Entity references as follows:
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:
![[RDF Data]](/fct/images/sw-rdf-blue.png)
