When captains went to sea in the 18th Century, computers, accurate chronographs, satellite imagery of weather, inertial navigation systems and GPS didn’t exist. Instead, the captain had a timepiece, compass, a Davis quadrant or a sextant, a chart and his knowledge of winds, weather and currents.
Navigation was both an art and a skill. To ensure that he was following his desired route from port A to port B, the captain needed to plot his position every day. To do that, one needed an accurate chart.
Portuguese explorers took detailed notes as they sailed down the coast of Africa in the 1500s. The data was kept as a state secret and unfortunately, most of their charts were destroyed in a tsunami caused fire that hit Lisbon in 1755.
In 1569, Geradus Mercator created what we now know as the Mercator Projection chart. First, Mercator figured out how to “flatten” the earth so one could draw a strait line (in navigation terms a rhumb line) on the chart. Second, he built on the work two Greek mathematicians – Erastothenes and Hipparchus – to draw lines of latitude and longitude on his new type of chart. Erastothenes invented what we know as latitude and longitude in the Third Century BC. Hipparchus followed in the Second Century BC by plotting latitude and longitude on a map of the known world.
The next step was to make Mercator’s charts widely available. Another Dutchman Lucas Waghenaer compiled and printed the first books of charts in 1584. His Spieghel der Zeevaerdt became the defacto standard and was translated into English in 1588 and became known as “waggoners” or “sea atlases.”
Accuracy was a problem because the data used to hand draw the charts came primarily from ship captains, not trained cartographers. How well they actually reflected the coastline was often lost in drawing the chart.
The next major step in moving cartography from an art to a science occurred when the French established the first national mapping agency – the Dépôt des Cartes et Plans de la Marine in 1720. It set standards for chart accuracy and nomenclature.
By the mid-18th Century, governments printed charts on linen backed paper so that they could be rolled and unrolled. Private publishers used a less expensive blue backing paper similar to what is used in Manila folders today to allow them to be rolled for storage. These charts were known as “bluebacks.”
American merchant seaman who went into French ports could purchase these charts and during the American Revolution, the Continental Navy had access to accurate (for the time) French charts of North America, the Caribbean and Europe.
The Brits waited until 1795 to create its Hydrographic Office and the U.S. established the Coastal Survey office in 1807. These government agencies had a significant advantage over over private mapmakers because they were given money and ships to send on surveying missions. These voyages by trained surveyors and cartographers led to the accurate charts we have today.