page_title: Benchmark (surveying)
hierarchical_section_title: Benchmark (surveying)
caption_attribution_description: English: An early Ordnance Survey benchmark - not the usual mark as not on a vertical face
context_page_description: The term benchmark, or bench mark, 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. These marks were usually indicated with a chiseled arrow below the horizontal line.
  The term is generally applied to any item used to mark a point as an elevation reference. 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. If an elevation is marked on a map, but there is no physical mark on the ground, it is a spot height.
  The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark. A fundamental benchmark is a point with a precisely known relationship to the vertical datum of the area, typically mean sea level. The position and height of each benchmark is shown on large-scale maps.
context_section_description: The term benchmark, or bench mark, 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. These marks were usually indicated with a chiseled arrow below the horizontal line.
  The term is generally applied to any item used to mark a point as an elevation reference.  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. If an elevation is marked on a map, but there is no physical mark on the ground, it is a spot height.
  The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark.  A fundamental benchmark is a point with a precisely known relationship to the vertical datum of the area, typically mean sea level. The position and height of each benchmark is shown on large-scale maps.
  The terms "height" and "elevation" are often used interchangeably, but in many jurisdictions they have specific meanings; "height" commonly refers to a local or relative difference in the vertical (such as the height of a building), whereas "elevation" refers to the difference from a nominated reference surface (such as sea-level, or a mathematical/geodetic model that approximates the sea level known as the geoid).  Elevation may be specified as normal height (above a reference ellipsoid), orthometric height, or dynamic height which have slightly different definitions.
caption: Occasionally a non-vertical face, and a slightly different mark, was used
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