Charting the unknown

Ever since the Age of Exploration, surveying has played a crucial role in the mapping of our world. This article delves into the captivating history of surveying at a time when GPS did not exist. When early explorers set sail to discover new lands, which surveying techniques were used and which challenges were overcome to help them navigate unfamiliar territories and create detailed maps?

Early explorers faced numerous challenges in their expeditions – from diseases to mutinies – and they had to tackle them without modern technologies that we often take for granted today. Navigation and mapping were particularly arduous tasks, relying heavily on rudimentary instruments, celestial navigation and dead reckoning. One of the primary challenges was to determine precise locations. Without GPS, explorers had to use tools like astrolabes, sextants and compasses to determine their position using the sun and stars. This method was heavily dependent on two factors: clear skies and a highly skilled navigator.

In the 1500s, determining the time of day was one of the main challenges that came with navigation, making it difficult to effectively determine longitude. Consequently, longitudes were often broad guesses, leading to inaccuracies in charts and therefore navigational errors. This challenge persisted until the creation of the marine chronometer in the 18^th century.

Early cartography was an art form. Cartographers translated explorers’ accounts of their travels into stunning images, often intended for publication in books and newspapers to inform the general population of the adventures. However, the harsh conditions and challenges faced by the explorers who provided the input meant that many of these maps were inaccurate and often speculative.

Early surveying techniques

The Age of Exploration (from the late 15^th century to the 17^th century) marked a significant period in history when continents united, and Europeans established routes to previously unknown worlds. One of the main motives for these expeditions was the establishment of new trade routes, which meant that accurate mapping and surveying became essential for success.

One of the first and most crucial tools used by early explorers was the compass. This provided a raw sense of direction, which had proven crucial in explorative navigation. To measure angles, explorers used instruments like astrolabes and cross-staffs. Astrolabes, dating back to ancient times, were useful for determining the altitude of celestial bodies. By measuring the angle between the horizon and the sun or stars, explorers could estimate their latitude. Cross-staffs were used to measure angles between distant objects on land, aiding in the creation of basic maps and charts.

Triangulation also played a key role in early surveying. Explorers and surveyors would establish a baseline between two points and then measure the angles to a third point from each end of the baseline. By applying trigonometric calculations, they could accurately determine the distances and positions of unknown points relative to the baseline. This process was repeated across vast areas to create a network of interconnected triangles, allowing for the accurate mapping of landscapes and coastlines. Triangulation provided a systematic and reliable method for surveyors to gather data and create detailed maps, enabling explorers to effectively communicate the raw characteristics of the terrain back to their countries.

Technological advancements

During the Age of Enlightenment (in the 17^th and 18^th centuries), the field of surveying experienced a series of developments that enhanced the precision and efficiency of cartography and navigation. One of the most notable innovations was the enhancement of the theodolite, which evolved from simpler devices like the plane circle. Originating from the work of the well-known 16^th-century English mathematician and surveyor Leonard Digges, who described it as the “instrumentum topographicum”, the theodolite was perfected during the Enlightenment to measure angles with high precision in both horizontal and vertical planes. The theodolite is equipped with a telescopic sight for targeting, and graduated circles for angle measurement, allowing for the precise determination of distances and elevations. The integration of clamps and slow-motion screws further improved the theodolite’s functionality, enabling fine adjustments and stable angle measurements. The improvements gradually made the instrument more practical and efficient for navigators and surveyors to take with them in their expeditions.

Another critical advancement was the widespread adoption of the sextant. The sextant’s design was improved with a movable arm (the index arm) and a scale (the arc) graduated to fractions of a degree. This provided navigators with a reliable means of determining their position, even in adverse weather conditions.

Like today, levels were an integral part of the surveyor’s toolkit, serving to establish horizontal lines and ensure accuracy in measurements. These devices consisted of a spirit level that housed a liquid-filled tube with an air bubble, with a level surface indicated by the bubble in the centre of the tube. Surveyors would position the level at various points along their surveying route, carefully adjusting its orientation to account for any slopes or variations in the terrain. By using levels in conjunction with other instruments, such as theodolites and chains, surveyors could create a consistent reference line for their measurements. The surveyor would position the level at a known point and align it horizontally, from which angles and height differences could be determined.

The Age of Enlightenment also saw significant advancements in the methodologies of triangulation and geodesy. Geodesists engaged in determining the Earth’s exact shape and size, which was vital for the development of accurate map projections and for understanding the planet’s physical characteristics. The efforts to resolve the debate between the Newtonians and the Cassinians over the Earth’s shape, through expeditions like the ones to Lapland and Peru, exemplify the period’s dedication to empirical, geodetic research.

These technological and methodological advancements during the Age of Enlightenment had a profound and lasting impact on the field of surveying. The period’s contributions to surveying laid the foundations for future developments (many of which did not occur until the 20^th century), setting the stage for modern practices. As a result, today’s surveyors can depend on detailed and accurate maps that form the basis of contemporary navigation and geographic information systems (GIS), and continue to shape our understanding of the world’s geography.

The life of a surveyor in the 1700s

Equipped with essential tools and a thirst for discovery, countless surveyors set out to map uncharted territories in the 1700s. In the days before satellite and GPS, these were the techniques and instruments they used:

The sextant

First, to establish their current position, surveyors used a sextant to measure the angle between a celestial object (like the sun or a star) and the horizon. This enabled them to calculate their latitude and longitude.

Reference points and theodolites

Next, the surveyors focused on establishing reference points. They employed a theodolite (a telescope mounted on a tripod) to measure both horizontal and vertical angles. By sighting reference points and noting their angles, they created a network of interconnected points. These reference points formed the foundation for their survey work.

Gunter’s chain

Surveyors ventured into the field armed with a metal chain. The so-called Gunter’s chain was exactly 22 yards (approx. 20m) long with 100 links. This gave the measuring of distances an element of consistency, besides being more reliable and durable than rope. Distances between the reference points created with the theodolite were accurately measured and documented.

Levels for precision

To account for slopes and uneven terrain, surveyors used levels. The levels were then often used with other instruments to gauge height differences over longer distances. By taking readings with the level, they adjusted measurements to ensure the highest possible accuracy.  

Conclusion

The exploration and mapping of the unknown world during the Age of Exploration was a remarkable feat accomplished by early explorers despite numerous challenges. The absence of modern technologies such as GPS, accurate timekeeping, reliable maps, and instant communication made their journeys incredibly perilous. They relied on basic tools and instruments like compasses, astrolabes and cross-staffs to aid their surveying efforts. As the Age of Enlightenment brought technological advancements such as the refinement of the theodolite, adoption of the sextant and progress in triangulation and geodesy, it revolutionized surveying and enhanced the accuracy of mapping. The legacy of these early explorers and their technological advancements is evident in the detailed and accurate maps we depend on today.

Surveying timeline

Technological advancements throughout the centuries have transformed surveying from a manual, labour-intensive process into a highly precise and efficient field that leverages electronic and satellite technology. Today’s surveyors can achieve levels of accuracy and efficiency that were unimaginable in the past, and the industry continues to evolve with ongoing technological innovations.

12^th century: First use of the magnetic compass in mining surveying in Harz, Germany.

16^th century: The plane table was invented by Gemma Frisius around 1530, and became widely known through J. Praetonius in the late 16^th century.

17^th century: Instruments like quadrants and astrolabiums, used for angle measurements, were notably improved by Snellius (in 1615) and Picard (in 1669-70). Picard also introduced telescopic sights allowing for more accurate angle measurements.

18^th and 19^th centuries: After evolving from earlier instruments, significant improvements were made to theodolites, including the introduction of telescopic sights and more precise angle measurement.

1947: Development of the geodimeter, an electronic distance measurement (EDM) instrument that used light waves to measure distances accurately over long ranges.

1957: Development of the tellurometer, another EDM device that used microwaves for distance measurement, further changing surveying from triangulation to trilateration.

1970s: This decade saw a number of key developments, including:

• The electronic tacheometer, an instrument that combined the functions of a theodolite and an EDM, allowing for rapid measurements of angles and distances.
• Doppler satellite receivers, which utilized the Doppler effect from satellites to determine positions on Earth, enhancing the accuracy of location-based measurements.
• Inertial surveying systems, which used gyroscopes and accelerometers to determine position without the need for external references (particularly useful in areas without clear sightlines).
• The launch of the first global positioning system (GPS) satellite in 1978 marked the beginning of satellite-based positioning, which has revolutionized surveying by providing precise location data anywhere on Earth.

Further reading

Holsen, J. (2015), ‘The Development of Survey Instruments’, The International Hydrographic Review, 61(1). Available at: https://journals.lib.unb.ca/index.php/ihr/article/view/23512 (Accessed: 30 June 2024).

Smith J.,De Graeva J. (2010), ‘History of Surveying’, FIG Publications