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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.

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.