Isaak de Graaf worked as a cartographer for the
Dutch East India Company (VOC). In 1705 he became the chief map maker for the VOC's
Amsterdam chamber, a position he held for 38 years, until 1743. The preparation and control of navigation charts was closely regulated within the VOC. Charts were produced for use by the company's ships and were not normally printed or sold publicly, helping to protect geographic knowledge used in the company's long-distance trading routes. In this role De Graaf produced manuscript navigation charts used by VOC ships operating within its trading network. Many of these maps were drawn by hand on
vellum, a durable material made from animal skin that could withstand use at sea. Many of De Graaf's charts were so-called passage charts (Dutch:
overzeilers), which guided ships across long ocean routes. One chart of the
Atlantic Ocean shows the sailing route followed by VOC vessels from the
Netherlands past
Madeira, the
Canary Islands and the
Cape Verde islands before crossing the
equator and continuing toward the
Cape of Good Hope. The charts included
compass roses and networks of
rhumb lines that helped sailors maintain a constant compass bearing when plotting a course across the ocean. Important points along the route were also marked, helping ships navigate areas near the equator where winds and currents could easily push them off course. Surviving charts attributed to De Graaf include maps of the Atlantic Ocean,
Sumatra, the
Sunda Strait, the
Java Sea and the northern coast of
Java. ==de Graaf map discovered==