Benchmark (surveying)

The term benchmark, bench mark, or survey benchmark originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future.Frequently, bronze or aluminum disks are set in stone or concrete, or on rods driven deeply into the earth to provide a stable elevation point.A fundamental benchmark is a point with a precisely known relationship to the vertical datum of the area, typically mean sea level.Prominent features on buildings such as the tip of a church spire or a chimney stack are also used as reference points for triangulation.These records are usually in the form of a geographically searchable database (computer or map-based), with links to sketches, diagrams, photos of the marks, and any other technical details.
An Ordnance Survey cut mark in the UK
Occasionally a non-vertical face, and a slightly different mark, was used
An Ordnance Survey flush bracket
BenchmarkSurvey markerOrdnance Surveysurveyorsleveling rodbroad arrowspot heightVertical positionvertical datummean sea levelelevationnormal heightorthometric heightdynamic heightTriangulation pointschurchchimney stacktriangulationUnited KingdomNational mapping agencyCanadaNatural Resources CanadaDenmarkDanishFranceInstitut Géographique NationalSurvey of IndiaMoroccoRepublic of IrelandOrdnance Survey IrelandIstituto Geografico MilitareGeospatial Information Authority of JapanNetherlandsRijkswaterstaatKadasterNew ZealandLand Information New ZealandPakistanSurvey of PakistanSouth AfricaDepartment of Rural Development and Land ReformInstituto Geográfico Nacional (IGN)Ordnance Survey of Northern IrelandUnited StatesNational Geodetic SurveyUnited States Coast and Geodetic SurveyUnited States Army Corps of EngineersUnited States Forest ServiceUnited States Geological SurveyStoperaNormaal Amsterdams Peilmanhole coverWashington MonumentTorontoOttawaBarcelonastatue of King Charles ITrafalgar SquareCharing Crosspoint from which distances from London are calculatedBenchmarkingLevellingOrdnance datumAtlas ObscuraWikisource1911 Encyclopædia Britannica