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What’s a Theodolite? A Not-So-Precise History

June 27, 2017
theodolite
Marc ChalufourA brass theodolite of unknown origin resides in the AMC Library & Archives collection.

The shiny brass theodolite in AMC’s Library & Archives was built by a British firm, likely in the late 1800s, but its exact provenance and its path to AMC remain unknown. Artifacts make up a small portion of AMC’s collection, but the theodolite’s relationship to AMC’s own history of cartography and trail building is strong enough to warrant its inclusion.

A theodolite is a precision surveying instrument that measures angles along vertical and horizontal planes. From those measurements, a cartographer can use triangulation to determine the distance between two points. The modern theodolite dates to the 16th century, and versions remain in use today, five centuries later, although digital technology has rendered the 21st-century model almost unrecognizable from its ancestors.

The legendary mountaineer Bradford Washburn used a theodolite, among other tools, to take measurements for his famously detailed Mount Washington map, published in 1988. Washburn relied on the aid of volunteers to help him trek his bulky equipment up, down, and around the mountain during a decade of surveying.

Not everyone has the luxury of that much time or labor. The trailbuilder J. Rayner Edmands presented a detailed mathematical paper, “The Identification of Distant Points,” in an 1879 edition of AMC’s journal, Appalachia. In the field, the cartographer should “aim to accumulate as much material as possible….Nothing is so satisfactory as actual measurement,” he wrote, before adding, “The accuracy of the theodolite is not needed.”


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Marc Chalufour

Marc Chalufour is the senior editor of AMC Outdoors.