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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bob Bossert
Date: 2025 Sep 5, 08:00 -0700
Since you are interested in historic sources, here are two sources I found on Google a few years ago. They both explain why Polyconic was used in some areas and Mercator in others. Maybe the NOAA archive can confirm when the switch over to Macator projection was made for key bodies.
“A Textbook on Coast and Lake Navigation” Copyright 1902 by International Textbook Company.
page 38:
The polyconic “projection is therefore advantageous for the representation of a coast line that runs north and south, or in the direction of the meridian, and is for this reason extensively used by the United States Coast and Geodetic Survey in the preparation of working charts of the coast, and also by the United States Engineer’s Office, War Department, in the preparation of charts used by mariners on the Great Lakes.”
page 43:
“Charts for Use on the Great Lakes….. Great Lakes charts published by the US Engineer Office are constructed on the polyconic projection… on the US Engineer chart only statute mile is used.”
From “United States Hydrographic Office”, “Great Lakes Pilot, Volume II” 1921 Government printing office.
Page 3
“On a polyconic chart, since a straight line represents (within the limits of 15 or 20 degrees of longitude) nearly the arc of a great circle, or the shortest distance between two points, bearings on the chart are identical with observed bearings. All Lake Survey charts are polyconic projections. The Mercator projection is unsuited for surveying purposes.”
