Natural navigation: The stick maps of the Marshall islands which were used by the Marshallese to navigate the Pacific Ocean by canoe. Unlike modern maps, stick charts are not literal representation of the sea, but more an abstract illustration of the ways that ocean swells interact with land. Indeed, individual charts varied so much in form and interpretation that many times a stick chart could only be read by the person who made it. Seashells depict the atoll and island locations. Atoll and island names are typed on strips of paper which are glued onto the wooden sticks. Each straight stick represents regular currents or waves around the low-lying atolls while the curved sticks depict ocean swells. Not everybody knew how to make or read the charts. It was a closely guarded secret, and the knowledge was only passed on from father to son. When making journeys, fifteen or more canoes would sail together in a squadron, accompanied by a leader pilot skilled in use of the charts.