A nautical chart can be described as an instrument that summarises the geographical features of the ocean floor and along the coastline, which facilitates seafarers in their endeavour to navigate their vessels to the intended destinations. In practice, the ocean is dynamic and her features change with the time of the day as well as the season. No nautical chart could provide all the necessary information. A nautical chart usually has icons and symbols for water depth, navigational hazards (such as sandbars and shallows), shorelines, land geomorphological features, human settlements and the like. Fluid dynamic information such as tidal range and current flow are usually provided in separate nautical publications.

Early Chinese nautical charts

In China, the early concept of a nautical chart was one that provided the locations of seaports or land features along the route, which invariably hugged the shoreline. Chinese junks always sailed within eyesight of the coast and therefore the name of the next port or land features were important to ascertain the ship’s position. One of the earliest extant nautical charts, the Haidao Zhinan Tu (《海道指南圖》), was published in the Ming Dynasty. It was a simple rendition of a curved line marked with the names of ports and land features along the south bank of the Changjiang River leading to the sea and then along the shoreline to Hangzhou Bay. Simple as it may look, the chart heralded increased maritime activities along the Chinese coast that required the aid of a chart to guide less experienced navigators sailing from the capital, Nanjing, to Hangzhou Bay.^[1]

A more serious effort in nautical chart making was the scroll commonly known as the Zhenghe Hanghai Tu (《鄭和航海圖》) produced supposedly to record the route taken by Admiral Zheng He in his famous expeditions to India and the East Coast of Africa. Drawn on a long scroll, the chart does not have correct north-south directions. However, for practical sailing guidance, a dotted line was drawn showing the route to be taken, while giving correct compass bearings from one reference point to the next. The chart is scattered with pictorial drawings in traditional Chinese style showing many important islands and land features, enabling the navigator to mark the vessel’s correct position. Considering the fact that many Chinese navigators were only given a “Compass Journal” (針路簿) to navigate their ships, the Hanghai Tu, with the added feature of pictorial landmarks, which must have been a significant added advantage, could have been adequate for an experienced Master to follow in the ship’s quest to the Indian Ocean and Africa.^[2]

Visible progress was made in making nautical charts towards the later Qing, as shown in the Coastal Navigation Map of the Hong Kong Region dated to early Jiaqing period. As more large foreign sailing ships arrived, and as Chinese coastal defence became an issue, more informative charts began to appear, even though the execution of these charts remained at traditional manuscript level.^[3] Charts started to give hydrographic information such as water depth, anchorage position, and distance to the nearest major towns. Sometimes information about hidden sandbars and the nature of seabed sediments was also given. Though still a far cry from a western nautical chart, in which the precise position of a point can be marked by longitude and latitude, and distance and bearings can be easily ascertained, the information available in these manuscript charts, relative to the earlier charts, was nevertheless a significant improvement for seafarers.

Contrary to popular belief, the first Chinese pre-modern nautical sea chart was produced in 1863 (2nd year of Tongzhi) by Hu Lin Yi (胡林翼) and Yan Shu Sen (嚴樹森) in the Chinese atlas Da Qing Yitong Yutu (《大清一統輿圖》).^[4] A chart was produced showing the exact course that Chinese ambassadors would take in visiting the Kingdom of Ryukyu (today’s Okinawa). Although a scale was not given, this could be calculated by the latitude on the chart. The modernity of this chart could be attributed to the fact that it was based on an earlier survey map - which was initiated by Emperor Kangxi and drawn by Jesuit priests - named Huangyu Quanlan Tu (《皇輿全覽圖》)^[5] published in 1719. The map itself used Sanson projection. Even though the Mercator projection would be ideal for nautical charts, the Sanson projection does at least render rectangular longitude and latitude grids towards the equator, and therefore the bearings measured on the charts could still be used for short voyages, such as from Fuzhou to Okinawa, making this Fuzhou/Okinawa chart one of the best Chinese charts published in woodblock print before actual hydrographic surveys were undertaken by Chinese surveyors.

The earliest nautical charts in China were produced by Chinese marine survey teams under the auspices of the Chinese Navy, but were managed by the Chinese Customs, which was run mainly by foreign expatriates.^[6] As such, charts were chiefly produced for international shipping. Charting therefore was concentrated from Shanghai, upriver of Changjiang, to other foreign concessions as far inland as Wuhan and Yichang. An example was one published in both Chinese and English mapping Changjiang near Nanjing, dated to 1923.

Portolan charts

The earliest known European nautical charts, usually referred to as Portolan charts, were produced by Venetians and Genoese, who had a monopoly of Mediterranean maritime trade during the 15th to 16th centuries. The word derives from portolano, an Italian pilot book with sailing directions, notes of headlands and navigational hazards.

The earliest of these charts have been dated to the 13th century. The charts were drawn on vellum made from calfskin or on parchment from sheepskin or goatskin. To provide a visual reference, a portolano was distinguished by its unique radiating lines for mariners to check their headings. These lines are called rhumbs or lines of bearings. The graphic was first referred to as wind roses, representing eight wind gods from eight directions. With the arrival of more accurate compasses, the radiating lines were increased to represent 32 directions to enable more distant travel by more precise directional refinement.^[7]

Apart from the compass directional lines, the biggest difference between a portolan and a Chinese manuscript nautical chart is that a portolan gives a scale, with which mariners can estimate the distance already travelled as well as the remaining distance. On a portolan, which was an instrument first developed in the Mediterranean, the distance between two points could be estimated by the rhythm of the stroke of the oars and the length of the vessel. Other features include using colours, such as a black cross to indicate a dangerous rock, red dots for shallow waters, with islands and rivers shown in different colours.

The Great Exploration of the 15th century started with mariners first using the portolan chart. As new land was “discovered” and voyages became profitable, there was huge demand for more accurate nautical charts and improved navigational techniques. Both areas made big strides in the ensuing centuries as European traders arrived at the far end of the Asiatic continent in great numbers. When they wished to have a lengthy stay, they would undertake hydrographic surveys as soon as circumstances allowed. The first official hydrographer of the British East India Company, Alexander Dalrymple, was thus sent from Madras in 1759 to collect maritime information and draw rough charts to assist the activities of British sailors along the Chinese coast.