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The Mapmakers: An Essay in Four Parts
Mapmaking
18th Century
The trends of the 17th century became realities in the 18th. Advances in technology, general acceptance of new mathematical and astronomical theories, and rigorous training schools for navigators and surveyors had an increasing impact on the accuracy of maps.
In New France, escalating tensions with England prompted renewed hydrographic surveys of the Atlantic coast and the Gulf of St. Lawrence by Testu de la Richardière (1730-41), Gabriel Pellegrin (1734-55) and Joseph Bernard Chabert (1750-51). In 1750, Chabert erected Canada's first observatory at Louisbourg for astronomical observations and the determination of longitude. Inland, the engineer Chaussegros de Léry, and his son of the same name, made good charts of the upper St. Lawrence through Lake Ontario to Detroit and Sault Ste. Marie. All of these men were competent marine and military surveyors using the latest methods (mainly triangulation) and instruments. The interior of New France did not fare as well since there were no trained surveyors on the La Vérendrye expeditions. Their maps were, in fact, redrafted Native cartography.
After the mid 18th century, map accuracy increased, primarily due to the development and manufacture of new instruments and stringent training in how to use them. In 1731, John Hadley invented the reflecting quadrant (really an octant), which rapidly replaced the Davis back-staff for latitude observation. The sextant, a finer instrument, was developed out of the octant in 1757. It came into common use before the end of the century and remained in use well into the second half of the 20th century. The invention of the artificial horizon (a box of quicksilver), by George Adams in 1738, made latitude observation possible on land where the real horizon was not visible. The invention of the octant and sextant also made it possible to make reasonably good calculations of longitude by lunar distance, a method invented by David Maskelyne in 1761.
The construction of good high power refracting telescopes made another, older method of longitude calculation possible, by observing predicted eclipses of Jupiter's moons. In 1766, tables based on the Greenwich meridian and showing lunar distance and the locations of Jupiter's moons were printed in the Nautical Almanac. These two methods required a great deal of skill and an up-to-date Almanac. It was not until John Harrison invented the marine chronometer and it was tested on James Cook's second voyage (1772-75) that the problem of longitude calculation was solved. The first use of the chronometer in Canadian waters was on Cook's third voyage in 1778. During the 1780s it was used in Newfoundland waters and reappeared on the West Coast with Vancouver's surveys (1792). That these were all British inventions helped to move that country to the forefront as a naval power.
The modern mapping of Canada began in 1778 when James Cook appeared on the West Coast and Philip Turnor was hired by the HBC to train surveyors and to begin mapping the western interior. Inland surveyors such as Turnor, Fidler and David Thompson carried an octant or a sextant, modern compasses, an artificial horizon of quicksilver, a powerful refracting telescope and, if possible, the latest edition of the Nautical Almanac. Their methods were all similar, consisting of control points and estimated distances over a course laid out along compass bearings. Thompson, who surveyed some 20 800 kilometres of Canadian territory, would set up control points at prominent places for which he calculated latitude with his sextant and longitude by Jupiter's moons. From these points he laid out compass bearings, which he followed by canoe, by horse or on foot, estimating the distances he traversed. By repeating this process he established a grid of control points linked by compass bearings and estimated distances. Since distances had to be estimated, Thompson would adjust them through control points established with his surveying instruments. Hills and mountain ranges in Thompson's surveys were depicted by hachuring and the direction of river flow by little arrows. Other topographic detail was simply sketched in. Native encampments were often noted, and on his Columbia River survey Thompson even gave a population estimate for each of the Native villages he passed. These methods produced very good reconnaissance surveys.
In coastal charting, a marine surveyor such as Cook or Vancouver would keep a careful record of the course of their ship. Distances were calculated by means of a log, and prominent features along the coast were triangulated. It was essentially the same procedure used by Champlain, but often from a moving ship and with far better instruments. Surveys of an intricate coastline such as that of British Columbia were done by triangulation from rowboats, using beacons set on shore. Drawings were sometimes made of prominent features or a profile of the coast was sketched as it appeared from the sea. Surveying in the 19th century achieved greater accuracy through the common use of the chronometer and crews sent out with measuring chains and theodolites. Cadastral, boundary and railway surveys required a new kind of accuracy not found in earlier maps.
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