Nearly 1200 kilometers of boundaries surveyed in 1685-1910, upon which stone walls were subsequently built, were measured using high-resolution LiDAR (Light Detection and Ranging) in the northeastern United States (New Hampshire and New York). The geomagnetic declinations at the time of the original land surveys of those stone wall-defined boundaries have been determined and compared with (i) current geophysical models (i.e., gufm1, IGRF12; United States Historical Declinations-USHD), and (ii) measured declinations (Bauer, 1902). With the exception of lower declinations (i.e., 1.5° eastward) in 1775-1810, the results of this study are in good agreement with gufm1 and IGRF12 geomagnetic declinations. This study yielded systematically higher declinations (i.e., up to 2.0° westerly) than the USHD values during 1750-1780. These results demonstrate that geomagnetic declination can be determined when durable, human-engineered structures on land (e.g., stone walls; roads) are accompanied by detailed historical documentation and accurate land surveys. An example of using old streets (1699) in Colonial Williamsburg, VA is also discussed. Precisions of the bearings along boundaries in the 17th-19th century land surveys used this study were typically better than ±0.30°.
Delano, John W. PhD, "Measurements of geomagnetic declination (1685-1910) using land surveys, LiDAR, and stone walls" (2019). Atmospheric and Environmental Science Faculty Scholarship. 5.