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The Benchmark Hunting Hobby

The creation of our national system of geodetic benchmarks and the establishment of marks for coast defense assets is described under another tab. But it should also be mentioned that hunting for these geodetic markers makes a fascinating and challenging hobby. is a website dedicated to the hobby of placing and retreiving "geocaches," boxes of materials that are hidden by hobbyists and then found by other geocachers following strings of clues left for them by the caches' owners. A subpart of this website is given over to the closely related hobby of benchmark hunting. The FAQ page of the benchmarking website is a good place to start learning about the benchmark hunting hobby.

Benchmark hunters often start by consulting this mapping website, which offers a graphical interface that maps, stae-by-state, all benchmarks that are in the federal (National Geodetic Survey-NGS) database, state-by-state. Clicking on a map "pin" that indicates a benchmark on these maps can open up a link to an NGS Datasheet for a given mark or to the webpage at that describes other benchmark hunters' past attempts at finding that mark. The example links given above refer to one of the benchmarks hunted and found by the author within the Boston harbor defense system--the disk at Ft. Ruckman in Nahant, atop the 12-inch guns of Battery Gardner. keeps track for you of the marks you have found or not found, and you can file web-based reports with NGS that update the "official" running history kept for each station. These NGS reports may actually be useful to surveyors, who sometimes use these marks in their daily work.

Information about these marks is indexed by PID (Permanent Identifier), a code in the form of two alpha and four numeric characters that is unique to each geodetic mark. [Technically, the term "benchmark" is reserved for marks that result from surveyed "leveling," used to fix the altitude of a given point. In hobbyist terms, though, the terms "benchmark" and "geodetic mark" are often interchanged.] The RUCKMAN RESET mark linked to in the last paragraph has MY0039 as its PID.

The NGS Datasheet for each mark contains the latitude and longitude of the mark (precisely for Adjusted marks and roughly for Scaled ones), plus a narrative description of how to locate the mark in the field. Some of these descriptions are precise and correct, while others contain errors, refer to outdated landmarks, or are quite vague. The fun of the hunt consists of solving the "puzzle" of the directions to the mark, finding it (which may involve a bit of digging), and documenting your work with description and photos so that the next hunter to come along has an easier time than you did.

The gallery at left shows some of the situations encountered while benchmark hunting. The pages of this website display many more.

Benchmark Hunting

A fun hobby that can be done with a compass and a tape measure, or may expand to using a whole range of specialized bits of equipment (metal detectors, GPS units, laser measurers, and a variety of tools for chopping and digging your way to the marks).