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A series of four maps of the Indian Ocean—one for each quarter of the calendar year—showing the direction and intensity of the winds, including around the seas of Southeast Asia. There are extensive explanatory notes.

Map of the Indian Ocean showing the currents (represented by arrows), including during the North East and North West monsoons. Numbers on the arrows indicate the current’s speed.

Chart of the Indian Ocean, showing climate and weather-related data, including around the seas and straits of Southeast Asia where trade routes are marked, along with monsoon and typhoon regions, and currents during the different monsoon seasons.

To aid navigation, this map shows small islands, shoals and reefs, maritime routes for use during monsoons or at particular times of the year, bathymetry (sea depth), past explorers’ routes, shipwrecks and text about monsoons, typhoons and currents.

Maritime routes had to be adjusted in response to the changing monsoon seasons, as is seen on this late 18th century map of the Indian Ocean. Drawings of the heads of children blowing—called ‘wind-heads’—are used to indicate wind direction.

Two maps of the Indian Ocean showing currents (represented by arrows) and winds (represented by letters A to F) during the monsoon seasons. Three routes—one old and two new—from the Isle de France (Mauritius) east to the Strait of Malacca are shown.

The arrows on this map mark the direction of the seasonal monsoons experienced in the South China Sea and Philippine Sea during the late 18th century. Each arrow has a label indicating the month.

Map of the Indian Ocean showing the currents (represented by arrows) and winds (represented with letters A to F) during the monsoon seasons. Three routes—one old and two new—from the Isle de France (Mauritius) east to the Strait of Malacca are shown.

Map of the Indian Ocean showing the currents (represented by arrows) and winds (represented with letters A to F) during the monsoon seasons. Three routes—one old and two new—from the Isle de France (Mauritius) east to the Strait of Malacca are shown.

Coloured borders on this map show the kingdoms of mainland Southeast Asia and the Philippines. Arrows marked on the sea to the west of the Philippines indicate wind direction during the monsoon seasons (with the months marked in French).

Map dedicated to William Cowper, whose coat of arms sits atop the cartouche. It features two horses holding a crest with three martlets (mythical birds used in heraldry). The cartouche also features Asian traders. Monsoons are marked on the map.

The arrows on this map show the direction of the seasonal monsoons: each arrow has a label, indicating the month. The northeast coast of Borneo is labelled ‘A Desart [desert/deserted?] Coast’, while the south is labelled ‘Pepper Country’.