Alexander Keith Johnston (1844-1879) was an explorer and geographer of Tanzania.
Born in Edinburgh, he was the only son of the cartographer and publisher Alexander Keith Johnston, elder (1804-1871). His father and private tutors trained him in cartography and geography, and worked for the firm of Edward Stanford from 1866 to 1867. He then travelled to Germany to learn German geographical techniques, returning to work in the London branch of his father’s company of W. & A. K. Johnston. He became a life-long member of the Royal Geographical Society, acting as their assistant curator and cartographer.
In June 1878 he was appointed leader of the Royal Geographical Society’s expedition to lakes Nyasa and Tanganyika. In November 1878 he left London, and reached Zanzibar in January and Dar es Salaam in May of 1879. Not long after, Johnston contracted dysentery and had to be carried during the expedition, but six months later he died from dysentery and malaria on 28 June 1879. He was buried beneath a fig tree, which had his initials and the date of his death carved on the trunk. Johnston’s family later arranged for a large granite table to be erected with his name on it over his grave, and is remembered on his father’s grave in Grange Cemetery in Edinburgh.
Many of Johnston’s maps can be found in various published works of the time, many by his father’s firm, but also through others, including the Royal Geographical Society’s Geographical Journal and the African section of Stanford's Compendium of Geography. His interest in exploration and discovery can be seen in his 1870 map of The Lake Region of Eastern Africa and of the Upper Nile Basin Showing the Sources of that River Recently Discovered by Dr Livingstone.