Land records · Parcel maps · October 6, 2026
What Is a Benchmark in Surveying? Elevation Marks
What is a benchmark in surveying? A fixed point with a known elevation, often a brass disk, used to set heights for surveys, flood work, and construction.
What is a benchmark in surveying? A benchmark is a fixed, stable point whose elevation is known relative to a vertical datum. Surveyors start from a benchmark to measure the heights of other points, such as a building’s floor, a road grade, or the ground at a property corner. Many benchmarks are brass or aluminum disks set in concrete, bridges, or bedrock and stamped with an identifier. This page is general land-records background, not legal advice.
Benchmark vs boundary monument
A benchmark is about height. A boundary monument, such as an iron pin or a section corner, is about horizontal position and ownership lines. Some marks serve both purposes, but most property corners have no published elevation, and most benchmarks say nothing about where a lot line is.
Where benchmarks come from
- National geodetic networks. Federal agencies set thousands of marks with published elevations and descriptions that tell you how to find them.
- State and county networks. Highway departments and counties set their own control for roads and mapping.
- Project benchmarks. A surveyor may set a temporary benchmark on a site, like a nail in a utility pole or a mark on a curb, to carry elevations during construction.
What a benchmark disk shows
A typical disk is stamped with the agency name, a mark designation, and sometimes a year. Many say not to disturb the mark and cite a penalty. The disk itself does not usually show the elevation; that is in the agency’s published datasheet, along with the datum, such as NAVD 88, and directions to the mark.
How benchmarks are used
| Use | Why a benchmark matters |
|---|---|
| Elevation certificates | Ties a building’s floor height to the flood map datum |
| Topographic surveys | Gives contour lines real elevations |
| Road and drainage design | Keeps pipes and grades flowing the right way |
| Construction layout | Sets floor and footing heights consistently |
| Subsidence monitoring | Tracks ground sinking over time |
For flood insurance, an elevation certificate relies on the surveyor connecting to a benchmark or to satellite positioning tied to the same datum.
Finding a benchmark near you
Federal survey control can be searched online by location, and datasheets describe the mark’s setting and history. Many old marks have been destroyed by road work or construction, so a listed mark may be gone. County surveyor or GIS offices may list local control as well.
If you find a disk on your property
Leave it alone. Disturbing a survey mark can be illegal and makes work harder for future surveyors. If construction threatens it, contact the agency named on the disk or the county surveyor so the mark can be documented or reset.
Benchmarks and GPS
Modern surveys often use GNSS receivers and real-time networks to get elevations without leveling from a benchmark each time. Benchmarks still matter as checks and for tying GPS results to the official vertical datum.
Bottom line
A benchmark is a stable point with a known, published elevation used as the starting point for height measurements. It is different from a boundary monument, which marks horizontal position. Benchmarks underpin flood elevation certificates, topographic surveys, and construction grades. Find county survey records via the Platbookmapper map.
What is a benchmark in surveying FAQ
What is the difference between a benchmark and a monument?
A benchmark has a known elevation; a boundary monument marks a horizontal position, such as a property or section corner.
Does a benchmark disk show its elevation?
Usually not. The elevation is in the agency’s published datasheet for that mark.
Can I move a survey benchmark on my land?
No. Disturbing a survey mark may be illegal. Contact the agency or county surveyor if it is in the way.
What is a temporary benchmark?
A point a surveyor sets on a project site, like a nail or chiseled mark, to carry elevations during the work.
Are benchmarks used for flood elevation certificates?
Yes. Surveyors tie building elevations to a benchmark or to GPS positioning on the same datum.