Nielsen, Niels. 1939. “Atlas of America Agriculture. Physical Basis Includingland Relief, Climate, Soils and Natural Vegetation. U. S. Department of Agriculture. Washington 1936, 231 S., 47X30 Cm. Pris: $ 17.”. Geografisk Tidsskrift 42 (januar). https://tidsskrift.dk/geografisktidsskrift/article/view/48259.