Geodetic control points are stamped with a variety of different markings and symbols to help surveyors identify them in the field.
Center marks, the simple symbols in the middle of a monument cap, indicate whether a monument is a vertical control point marking a precise elevation (commonly referred to as a bench mark), a horizontal control point established at a known latitude and longitude (commonly referred to as a station or mark), a reference marker, or something else entirely.
We’ve highlighted the various types of control points along with their corresponding marks and symbols for handy reference below.
Note: This guide covers the center marks commonly used today, however, it is by no means an exhaustive list of all center marks known to surveyors. The following resources offer more detailed information about historical survey markings their uses in the field:
All of the center markings covered in this guide can be stamped onto Berntsen’s survey monuments. Learn more and browse our selection of monuments here.
Open triangle, or with dot or “+” sign
Horizontal control mark
- These marks can denote one of several types of horizontal control marks, depending on the particular horizontal control system that was used in establishing them and the amount of precision they represent. A triangulation station, for example, is positioned by measuring distances and angles from other stations. These are typically associated with nearby reference mark disks and an azimuth mark disk.
“+” symbol or center punch
- These markers are used to calibrate electronic distance measuring equipment. Markers with a “+” in the middle are used to mark distances of 0, 150, 430, and 1400 meters. Those with a center punch are used to precisely mark 100 feet from the “0” marker. Since these markers are only used for calibration, accurate horizontal or vertical positions are normally not available. Calibration baseline data can be accessed on the NGS website here.
Horizontal arrow with vertical slash
- Two or more reference marks are typically associated with a triangulation station. While these help preserve the location of triangulation stations, they are not actually geodetic control marks. The center arrow is supposed to point toward the triangulation station.
Gravity control mark
- These are used in gravity surveys, which can be placed indoors or outdoors. When set outdoors, these markers are usually be set in a concrete monument, bedrock, or a large structure.
Long horizontal line with short vertical line
Vertical control marks (bench marks)
- This style marker was a replacement for the USC&GS geodetic bench mark disk and is used for vertical surveys. The primary data for this type disk would be its elevation determined by differential leveling.
Circle or circle with dot
Topographic station mark
- These are bench marks used to conduct topographic surveys, which map ground features and contours.
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