Glacial movement tens of thousands of years ago formed the coasts of what are now Vancouver Island, British Columbia and Alaska. They are filled with inlets, peninsulas, and numerous small islands. Charting even a small portion takes time and patience – it took many years of expeditions under the flags of several nations to take measurements and create charts of the Pacific Northwest.
Charts were created with the process of hydrographic survey. Running surveys could be carried out from the ship. Using nautical navigational instruments like the chronometer and the sextant to determine a global position, navigational officers kept careful records of the ship’s course and speed so they knew their relative location when they took their bearings on the features of the coastline. By taking one bearing on a feature as they approached it and another as they left it behind, they could plot lines that crossed and fixed the position of that point of land. Land-based surveys could be carried out with greater detail and accuracy, using distance measurements and geometry. A chain was used to measure out a baseline of a known length. Angles were measured from each end of the chain to a large number of different points along the coast, and triangulation could be used to set out further baselines, extending the survey.
A process known as sounding measured the depth of the water by lowering a lead-weighted sounding line into the ocean. The line was marked in fathoms, a measurement equal to 1.83 metres. Sounding was often carried out from small boats that rowed in a straight line between two survey points. Smaller vessels were better suited to survey work, and the primary survey ship was often the smallest of the two or three sailing as part of an expedition. Greater manoeuvrability allowed vessels like schooners to take the narrow inland passes and tack into the wind for circumnavigation of small islands.
Although many expeditions produced rough maps at sea, at the end of the voyage, the captain handed over the hydrographic survey team’s notes, observations, and sketches of the coastline to a cartographer for the creation of the actual chart. Mistakes in measurements and positioning often resulted in errors in the early charts of 18th century expeditions to the Pacific Northwest, but these were corrected over time. The Spanish were often prevented by their government from publishing hydrographic information that could be used by other explorers. Cooperation among expeditions, however, produced higher quality charts in a shorter period of time. For example, Captain Vancouver, sailing on behalf of Britain, and Captains Galiano and Valdés, sailing on behalf of Spain, cooperated in their survey of Desolation Sound and the passage between the mainland and Vancouver Island.
Access to nautical information in the form of one-of-a-kind, hand-drawn charts, notes, and drawings was limited until engravings of charts were printed with presses that allowed for widespread distribution. When Vancouver returned from his voyage to the Pacific Northwest in 1795, he gathered his surveys, along with those of Spanish and Russian expeditions to areas he had not visited, in order to publish an atlas of the region. It remained the most important source for navigators to the remote regions of the coast through much of the 19th century.