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. These marks were usually indicated with a chiseled arrow – specifically a broad arrow – below the horizontal line. A benchmark is a type of survey marker. 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.

Purpose

The

height Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is). For an example of vertical extent, "This basketball player is 7 foot 1 inches in height." For an e ...

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 A mean is a quantity representing the "center" of a collection of numbers and is intermediate to the extreme values of the set of numbers. There are several kinds of means (or "measures of central tendency") in mathematics, especially in statist ...

. The position and height of each benchmark are shown on large-scale maps. The terms "height" and "

elevation The elevation of a geographic location (geography), ''location'' is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational equipotenti ...

" 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 Normal heights (symbol H^* or H^N; SI unit metre, m) is a type of height above sea level introduced by the Soviet scientist Mikhail Molodenskii. The normal height of a point is defined as the quotient of a point's geopotential number ''C'' (i.e. it ...

(above a reference ellipsoid), orthometric height, or dynamic height which have slightly different definitions.

Other types of survey marks

Triangulation points, also known as trig points, are marks with a precisely established horizontal position. These points may be marked by disks similar to benchmark disks, but set horizontally, and are also sometimes used as elevation benchmarks. Prominent features on buildings such as the tip of a church spire or a chimney stack are also used as reference points for

triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle m ...

. In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, triangulation points are often set in large concrete markers that, as well as functioning as triangulation points, have a benchmark set into the side. With the increasing use of GPS and electronic distance measuring devices, the same techniques and equipment are used to fix the horizontal and vertical position of a survey marker at the same moment, and therefore the marks are usually regarded as "fixed in three dimensions". Flush brackets are metal plates placed flush into the faces of buildings or other structures. Although many are attached to triangulation pillars as above, Non-Pillar Flush Brackets were also frequently located in the faces of buildings.

Agencies responsible for benchmarks

Benchmarks are typically placed ("monumented") by a government agency or private survey firm, and many governments maintain a register of these marks so that the records are available to all. 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. Government agencies that place and maintain records of benchmarks include: *

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

** Natural Resources Canada (Geodetic Survey Division) *

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

** GST () *

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

** ( IGN on Wiki FR). *

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

** Survey of India *

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

** ANCFCC *

Republic of Ireland Ireland ( ), also known as the Republic of Ireland (), is a country in Northwestern Europe, north-western Europe consisting of 26 of the 32 Counties of Ireland, counties of the island of Ireland, with a population of about 5.4 million. ...

** Ordnance Survey Ireland *

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

** Istituto Geografico Militare *

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

** Geospatial Information Authority of Japan (GSI) *

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

** Netherlands Partnership Geodetic Infrastructure (NSGI) *** Rijkswaterstaat (vertical) *** Kadaster (horizontal) *

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

** Land Information New Zealand *

Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...

** Survey of Pakistan *

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

Department of Rural Development and Land Reform The Department of Rural Development and Land Reform was, from 2009 to 2019, one of the departments of the South African Government of South Africa, government. It was responsible for topographic mapping, cadastre, cadastral surveying, Recorder of d ...

Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...

** Instituto Geográfico Nacional (IGN) *

Ordnance Survey The Ordnance Survey (OS) is the national mapping agency for Great Britain. The agency's name indicates its original military purpose (see Artillery, ordnance and surveying), which was to map Scotland in the wake of the Jacobite rising of ...

** Ordnance Survey of Northern Ireland *

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

** The National Geodetic Survey (NGS; formerly

United States Coast and Geodetic Survey The United States Coast and Geodetic Survey ( USC&GS; known as the Survey of the Coast from 1807 to 1836, and as the United States Coast Survey from 1836 until 1878) was the first scientific agency of the Federal government of the United State ...

) ** The

United States Army Corps of Engineers The United States Army Corps of Engineers (USACE) is the military engineering branch of the United States Army. A direct reporting unit (DRU), it has three primary mission areas: Engineer Regiment, military construction, and civil wo ...

(USACE) ** The

United States Forest Service The United States Forest Service (USFS) is an agency within the United States Department of Agriculture, U.S. Department of Agriculture. It administers the nation's 154 United States National Forest, national forests and 20 United States Natio ...

** The

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

(USGS)

Notable benchmarks

* The brass benchmark in the Amsterdam Stopera (combined city hall and opera house) is a tourist attraction, since the benchmark below the Dam square, which has been used for the zero level of Normaal Amsterdams Peil (NAP) in the

, is concealed by a manhole cover. The latter benchmark has been used also for the national zero level of other countries in northwest Europe as well as for the European Vertical Reference System (EVRS). * Benchmark A in Washington, D.C. is miniature replica of the

Washington Monument The Washington Monument is an obelisk on the National Mall in Washington, D.C., built to commemorate George Washington, a Founding Fathers of the United States, Founding Father of the United States, victorious commander-in-chief of the Continen ...

. Installed in the late 1800s, this benchmark was used during the construction of the Monument and in subsequent surveys performed by the NGS. Upon completion of the monument grounds, Benchmark A was buried in a brick-lined pit and concealed by a manhole cover. In 2019, the "mini monument" was unveiled to the public for a brief time before being covered back up again.

Image gallery

USCGS-E134.jpg,

benchmark disk in the

Bench mark at Saint Goussaud, Limousin, France, by Institut Geographique National.jpg, Bench mark at Saint Goussaud, Limousin, France, by Torontobenchmark.jpg, City of

Toronto Toronto ( , locally pronounced or ) is the List of the largest municipalities in Canada by population, most populous city in Canada. It is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a p ...

benchmark disk in

Point Géodesique no. 2378, Terres et Forêts Québec (cropped).jpg, Benchmark disk in

Ottawa Ottawa is the capital city of Canada. It is located in the southern Ontario, southern portion of the province of Ontario, at the confluence of the Ottawa River and the Rideau River. Ottawa borders Gatineau, Gatineau, Quebec, and forms the cor ...

, Ontario, Canada File:Barcdock1.jpg, Vial Moll de Bosch i Alsina, near Port de Barcelona building, & pedestrian crossing

Barcelona Barcelona ( ; ; ) is a city on the northeastern coast of Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second-most populous municipality of Spain. With a population of 1.6 million within c ...

File:Charing Cross benchmark.jpg, Benchmark on the plinth of the statue of King Charles I in

Trafalgar Square Trafalgar Square ( ) is a public square in the City of Westminster in Central London. It was established in the early-19th century around the area formerly known as Charing Cross. Its name commemorates the Battle of Trafalgar, the Royal Navy, ...

, London: the site of the medieval

Charing Cross Charing Cross ( ) is a junction in Westminster, London, England, where six routes meet. Since the early 19th century, Charing Cross has been the notional "centre of London" and became the point from which distances from London are measured. ...

, and the point from which distances from London are calculated File:PylonBenchmarkNMKT.jpg, Benchmark painted on an electricity pylon's foundation File:Dorfkirche Flemsdorf 2020 Vermessungspunkt.jpg, Benchmark of the Prussian Survey Authority on a church in Brandenburg

References

External links

{{EB1911 poster, Bench-mark
Canadian Spatial Reference System

History of the Canadian Geodetic Survey Division

UK benchmark database

Detailed description of the different types of UK benchmark

US NGS Benchmarks overlaid on a Google Map

Benchmarks and levelling points

Benchmarks in the UK, mostly Gloucestershire, plus Gibraltar & Barcelona
Surveying and geodesy markers Vertical position