The most profitable commodity produced in the colonies was sugar, and the plantations of Jamaica created a vast amount of wealth for British merchants. Jamaica became the center of the Caribbean sugar trade by the 18th century; however, unlike the mainland colonies, the island never became self-sufficient – it existed only for the production of the crop. This 1780 chart of Montego Bay and Port Antonio shows two areas of the island that were dedicated to the export of raw sugar. Safe navigation of these ports was essential to the continuation of the sugar trade, and Britain made a point to conduct hydrographic surveys of the area, as they did on the mainland.