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Map of the Gaspar Strait, off the east coast of Sumatra. The web of lines is a rhumbline network, numbers indicate sea depth (bathymetry), and there are side views of islands (elevations), all to aid navigation. Five 18th century routes are marked.

Hand-drawn portolan (nautical) chart, featuring a rhumbline network (the web of interconnected lines), bathymetry (sea depth), shoals and reefs, and names of coastal settlements, all to aid navigation. With a colourful compass rose.