Scottish geographer, first hydrographer of the British Admiralty and proponent of the existence of a vast, populous continent in the South Pacific, which he called the Great South Land.

Dalrymple spent most of the time between 1757 and 1764 in the East Indies trying to further trade for the East India Company and became the company's hydrographer in 1779. Recommended by the Royal Society of London to lead an expedition to the South Pacific to observe a transit of Venus (1769), Dalrymple hoped to find the Great South Land in the course of his voyage. But command of the expedition went instead to Capt. James Cook (Cook, James), who returned without having sighted the continent.

In 1770–71 Dalrymple published his twovolume Historical Collection of the Several Voyages and Discoveries in the South Pacific Ocean, in which he continued to assert the existence of the continent. The book aroused wide popular interest, and on his next voyage Cook again went in search of the Great South Land. When Cook returned with proof that the continent did not exist, Dalrymple became his bitter opponent, eventually attacking him in print.

From 1795 until his death, Dalrymple was hydrographer to the Admiralty. As such, he organized its hydrographic department and collected and published many valuable ocean charts.