When you look up the list of important cartographers in Wikipedia, there are 18 names listed for the first 2'000 years up to 1400 AD. 17 names for the 15th century. More than 100 for the 17th century. The number of cartographers exploded indeed. The first 18 were Greek, Roman, Chinese and Indian. The next 17 mostly Italian and German. The following 38 mostly Portuguese and Dutch. Let's return to this later.
Italian Map of the Mediterranean early 16th century
How did this explosion of cartographic knowledge happen? And how could cartographers suddenly draw such precise maps when nothing equivalent existed before? What was the innovation behind this development? Looking at the map above we recognise the distinctive features of the North African, Spanish, French and Italian coast as well as the shape of the islands of Corsica, Sardinia and Sicily. How did they do it? By combining data from compass and astrolabe readings in ship logs with the duration of a ships journey.
Design of a European compass early 14th century
Compasses arrived in Europe with the Mongols. Whether they travelled in the bags of explorers like Marco Polo or reached us via Arab merchants who knew the east much better we will never know. The technology was already 1'000 years old by the time it reached Europe. It was used by Chinese mariners during the Han Dynasty (contemporary to the Roman Empire). What started first as a magnetised needle floating on a bowl of water developed into a dry, portable compass. The first written records of its use in the Mediterranean date back to 1310.
At around the same time, the Europeans also discovered how to measure speed when at sea. A string of knots (the distance between knots was fixed) was thrown overboard and the number of knots travelled for a given time counted. The ever present sand hour glass on ships allowed for precise measurement of time. With direction and distance travelled it was possible to establish one's position on open sea if the point of departure was known. As the ship's captains kept log books with all these details and hourly measurements, they created a huge body of valuable data that never existed before.
Replica of a Persian Astrolabe - it copies an instrument from the 16th century
The European Mariners had another tool at their disposal which was invented by the Greek around 200 BC: the Astrolabe. The tool combined measurement and calculations and allowed the fixation of the sun's and the moon's precise position. Determining the precise latitude became possible. Whilst not absolutely necessary to fix a position if speed, direction and point of departure are know, the Astrolabe provided some valuable data for checking the result of the first calculation.
Protolean Chart from 1489
For map makers, the ship log books were a gift from heaven. Whist mostly useless for the ship's captains once they returned home, the cartographers wold buy these log books and would use their data to calculate the position of ports, prominent features on the coast lines such as mountains, bays, peninsulas. Using several dozen log entries for - let's say the trip from Brindisi to Durres - allowed them to adjust the positions for different wind speeds and weather conditions. The high number of data points allowed the map makers to calculate accurate average position points which they then transferred on maps. It was a painstaking and tedious process but it worked. Suddenly, people back home in Venice, Genoa or Spain could plan their journey with accuracy and captains could be given specific instructions. The fact that Venice became a centre for printing books so soon after Gutenberg's invention in 1439 also helped. Like books, now hundreds of copies of maps could be printed from carved copper plates. For shipowners, maps became affordable and available.
Whilst maps provided a good sense of direction and location, they were not precise enough yet for navigating close to the coast at night or in bad weather. As long as longitude could not be precisely measured, nobody know where exactly they were. Avoiding a cliff requires precise information though. The Longitude Problem was eventually solved by the British watch maker John Harrison. His chronometer was so precise that after two Atlantic crossings the clock time deviated only by 1 second from real time. By measuring the time difference between real noon time and midday of the departure port (shown on the chronometer), longitude could be calculated. But all this happened only in 1740 - and not in the Mediterranean.
In the 16th and 17th century, the galleys thus continued to hug the coast line and "hopped" from port to port. There was no alternative. But the ground breaking innovation of precise maps was made in the Mediterranean - when you look at google maps on your iPhone today remember where it all came from.
Comments