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Nautical charts, like this late 18th century example of the north-west coast of Borneo, were designed to help ships navigate. The numbers marked along the coastline and sea routes indicate the depth of the sea (bathymetry).

Nautical charts like this are detailed around the coasts and on the seas (e.g. river mouths, islands, shoals and reefs) while the interiors are blank. The web of lines is a rhumbline network, while the numbers indicate sea depth (bathymetry).

A map of the China Sea between Malaya, Sumatra and Borneo. The numbers indicate sea depth (bathymetry), and there are drawings of the side views of some of the islands (elevations), both used to aid navigation. Some maritime routes are also marked.