This chart of the Indian Ocean and East Indies was printed on vellum. Only three other copies are known to exist. It shows European discoveries of the Australian continent made before Tasman. Jacob Aertsz Colom based the information on a map produced by Hessel Gerritsz, chief cartographer of the Dutch East India Company. A primary compass rose sits in the centre of the chart, surrounded by 16 secondary compass points. The rhumb lines, interconnecting the compass points, were used to aid navigation and measure a course to be steered.