European states treated accurate charts as strategic information, illustrated by Spanish restrictions and the value of charts captured by an English privateer in 1681. Trading companies and individual chartmakers gradually expanded systematic coverage. The Mercator projection, introduced in 1569, represented constant-bearing courses as straight lines and simplified course plotting. Distance measurement remained awkward enough, however, that simpler plane charts stayed common into the eighteenth century.
Chapter · 3:20:26-3:22:18
Chart secrecy and the slow adoption of Mercator navigation
A compact navigation history links secret imperial charts, captured Spanish sailing directions, commercial chartmaking, and the delayed practical adoption of the Mercator projection.