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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 brightly-coloured hand-drawn map of the Gulf of Siam, made for a ship’s captain. The elaborate compass roses are the centre of a rhumbline network, a web of lines to aid navigation. Bathymetry (sea depth), islands, shoals and reefs are also marked.