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finds ("recovers") the location of the mark, can then be uploaded to a website as proof of a find. Surveyors use the term "recovering" as a synonym for "finding" a mark. This does not mean that the found mark should be disturbed in any way. On the contrary—disturbing a survey mark in even a small way often destroys its usefulness to surveyors and others. In the U.S., benchmark hunters often reports on marks they find to the NGS database. It describes the mark's found/not found status, photos, current condition, and updated directions to reach it so that others (particularly surveyors) can easily re-find the mark.
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While many are accurate to within 100 feet, some are located as far as 3,000 or 4,000 feet away from the mark they refer to. This makes it difficult to locate them using a handheld GPS unit. Most marks have clear descriptions for how to reach them, but some lack complete descriptions. Additionally, changes in the surrounding buildings, roads, or terrain over decades may make the descriptions obsolete, as some marks have been removed due to construction or buried over time.
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with a triangle are known as "triangulation station disks" since they mark the position of the primary point used for triangulation (or map-making). Disks marked with an arrow are called reference marks (RMs) since they point (or "refer") to the principal station that may be located many feet away. A triangulation station often had two or three reference marks. Reference marks were set to enable the primary station to be re-established (or re-set) if needed.
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into the ground and possibly surrounded by a capped metal or plastic pipe that can be engraved and stamped like disks. Disks can also be set in rock ledges or boulders and in the concrete of a large structure such as a building, bridge abutment, or the base of a tower. In the UK, the mark is usually carved into a wall, or on a metal plate set into a wall.
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Care must be taken to ensure that a found disk is the one described on the data sheet, so as to avoid false reports. A reference mark may be mistakenly reported as the station mark. A disk set in 1945 may be confused with a similarly named disk that was set in 1946 by a different agency, and so on. A
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In the U.S., a survey disk is usually engraved with the name of the agency that placed it. The name of the mark (or the "station" it locates) is usually stamped into its surface, along with the date on which it was set (or re-set, since markers that have been destroyed, can be replaced). Disks marked
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As part of triangulation networks, intersection stations were sighted. They are typically tall, prominent, and well-defined points like a smokestack, the peak of a water tower, or a church spire. However, many of these objects have been altered or replaced by similar nearby structures and no longer
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vary considerably from one country to another. In the U.S., they are usually bronze discs about 3.5 inches in diameter. A typical disk is slightly inset into the top of a concrete pillar set vertically with its surface flush with the ground or projecting slightly. Others are metal rods driven
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of a mark that has adjusted coordinates. Metal detectors are useful for finding marks that have become deeply buried over time. The use of several of the tools in combination is sometimes required, but many marks are set on the surface of sidewalks, buildings, walls, boulders, or monuments and can
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Some of these marks have precise coordinates, including latitude and longitude, that are accurate to millimeter precision. Others, typically true elevation benchmarks, have only coordinates that have been scaled from a map. Scaled coordinates, unlike surveyed ones, were read from a topographic map.
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In addition to the survey data sheet for a mark being hunted, many hunters bring along a digital camera to take close-up and area pictures of the survey mark (a disk, a cross-cut in a rock, an old copper bolt, etc.). These photographs, as well as a current description of the mark by the person who
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Benchmark hunters also frequently carry a compass (to follow directions gleaned from the datasheet), a probe (like a long-bladed screwdriver) to search for buried marks, a trowel (or a small shovel) to uncover buried marks, a whisk broom (to clear away debris), and one or more tape measures of
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Each NGS-listed mark has a permanent identifier (PID), a six-character code that can be used to call up data about that mark on the
National Geodetic Survey website. Other websites offer maps of the locations (and PIDs) of marks in each individual state of the U.S. Until 2023,
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UK benchmarks tend to be on the corners of pubs, churches, and other public buildings, as well as farm buildings, railway bridges, and private houses especially those near a road junction. However, any building may be used, as well as natural features such as a rock outcrop.
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There are 6550 such pillars listed in the T:UK database. While most of them have fallen into disuse, about 184 of them are currently used in the
Passive Station network. These are maintained so they can be used as accurately located anchor points for
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Many survey markers in the U.S. were set over 100 years ago. There was a surge in creating these marks in the U.S. from about 1930 to 1955, in conjunction with the expansion of map-making activities across the country.
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Sometimes a survey mark is made much easier to find by the presence nearby of a witness post, a stake (or a small sign) driven into the ground, and used to draw attention to (and to warn against disturbing) the mark.
60:, the activity has become popular since 1995, propelled by the availability of online data on the location of survey marks (with directions for finding them) and by the rise of hobbyist-oriented websites.
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in the UK, but there is considerable overlap in participation. "Trig points" is the common name for "triangulation pillars". These are concrete pillars, about 4 feet tall, which were used by the
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In the U.S., markers are often found at the summits of mountains, along ridge lines, or on bare rock ledges with commanding views, because such sites provide good vantage points for
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In the U.S., about 740,000 benchmarks with precise elevations or coordinates (but only a small fraction of the existing survey marks) are listed in a database maintained by the
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reset elevation benchmark should not be reported as the original. Sorting out these differences and reporting them correctly is an important part of the hobby.
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Benchmarks are often located on private property, or access to them can only be achieved by crossing privately owned land, so permission is needed for access.
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U.S. benchmarks were commonly placed on public buildings, such as courthouses, post offices, city halls, and older schools.
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U.S. elevation benchmarks were often placed along rail lines or roads that provided good sight lines for leveling.
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The cartoon character Marvin Marker is based on a benchmark and was created to help preserve benchmarking in 1960.
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comparisons and are re-surveyed every five years to calibrate for any geological movements of the ground.
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on the top of the pillar, accurate bearings to nearby trig points could be taken. This process is called
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In the United
Kingdom, "trig-pointing" is a recreational activity similar to benchmarking. Searching for
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394:"No hiding from its popularity: At 20, Geocaching still seeks to turn players on to worldwide game"
354:"BOTTLES, POTS, & PANS? – MARKING THE SURVEYS OF THE U.S. COAST & GEODETIC SURVEY AND NOAA"
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in 1807 was to survey the coast of the United States in order to promote safe maritime commerce.
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A common location is the top level of the abutment of a highway bridge or its wing walls.
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See the network accuracy estimates per FGDC Geospatial
Positioning Accuracy Standards.
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various lengths, used in taping out referenced distances found on the data sheets.
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Yahoo! Group devoted to the study of the
Ordnance Survey triangulation network.
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in order to determine the exact shape of the country in a project known as the
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Live UK Benchmark
Database, primarily focusing on flush bracket benchmarks
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499:"Release Notes (Website: Benchmarking retirement) - October 17, 2022"
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UK Ordnance Survey benchmark source database, not updated since 1975
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mark the original location, so careful identification is required.
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81:(NGS) and accessible online. The majority of marks are set by the
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Handheld GPS receivers are often used to get within a few yards
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The benchmark hunting portion of the
Geocaching.com website.
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A person taking a photo of a located benchmark on a statue
52:, but hobbyists often use the term benchmarks to include
126:often be found without the need for special tools.
101:had a section of its site devoted to benchmarking.
36:, is a hobby activity in which participants find
623:UK images of Benchmarks (mostly Gloucestershire)
527:. National Geodetic Survey. mark with PID AH0147
159:Typical metal rod or stake benchmark, in Texas
474:"Benchmark Map Viewer - By Scaredy Cat Films"
171:Benchmark in Saint Goussaud, Limousin, France
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377:: CS1 maint: multiple names: authors list (
328:"Benchmark Hunting is the New Geocaching"
251:flush bracket on the corner of a wall of
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606:US benchmarks overlaid on a Google Map
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253:the Church of Saint Andrew the Apostle
91:United States Army Corps of Engineers
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392:Schlosser, Kurt (August 19, 2022).
525:"NGS Datasheet Sample PIDS Choice"
326:Garner, John (November 15, 2021).
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281:retriangulation of Great Britain
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611:New England Benchmarks web site
183:Vial Moll de Bosch i Alsina in
83:United States Geological Survey
56:or other reference marks. Like
478:benchmarks.scaredycatfilms.com
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648:Surveying and geodesy markers
352:Leigh, CDR George E., Ret'd.
271:is more popular than hunting
73:Sources of data on U.S. marks
439:The original mandate of the
87:United States Forest Service
552:Monkey Mountain Company.com
548:"History of Survey Markers"
462:. National Geodetic Survey.
423:Mountain Monkey Company.com
419:"History of Survey Markers"
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219:lines to distant points.
79:National Geodetic Survey
616:April 25, 2012, at the
46:geodetic control points
643:Outdoor locating games
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130:Description of markers
54:triangulation stations
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601:UK Trigpoint Database
456:"Datasheet PIDS Form"
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558:on January 24, 2022
441:Survey of the Coast
429:on January 24, 2022
505:. October 17, 2022
303:In popular culture
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638:Individual sports
503:Geocaching Forums
332:Millennial Cities
211:Typical locations
34:benchmark hunting
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509:November 7,
363:January 19,
269:trig points
632:Categories
359:. NOAA.gov
313:References
285:theodolite
273:benchmarks
259:in England
143:A typical
58:geocaching
38:benchmarks
483:April 17,
239:In the UK
185:Barcelona
147:Benchmark
50:elevation
614:Archived
398:GeekWire
373:cite web
64:History
531:May 5,
89:, the
357:(PDF)
145:USCGS
564:2021
533:2024
511:2023
485:2024
435:2021
405:2023
379:link
365:2013
339:2023
16:Game
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
