U.S. Coast Survey A.D. Bache Supdt. Magnetic Declination (Variations of the Compass) Isogonic Lines for the year 1870

A nice overview map showing the Magnetic Declination isogonic lines that will be used starting in 1870.

IMPORTANT NOTE:

All of our United States Coast Survey (USCS), United States Coast & Geodetic Survey (USC&GS), and similar maps and charts have been professionally unfolded and flattened using humidity baths, semi-permeable membrane, and drying blotter techniques. Most others you typically see on eBay have not been, and worse, are quickly and crudely unfolded for the low-quality photos you see. Unfolding these maps in that way is damaging and weakens them. Please be aware.