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Three maps of the Caroline Islands. One shows colonised areas in Southeast Asia: Dutch East Indies; British North Borneo, British New Guinea; German New Guinea; Philippines (Spain); Portuguese Timor. The route of the Challenger expedition is marked.

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.

Southeast Asia is shown on sheets two and three of this 12-sheet map of the Indian and Pacific oceans, including detailed inset maps of the straits of Singapore, Bangka, Gaspar and Sunda, with bathymetry (sea depth), shoals, reefs, anchorages etc.

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.