Terra incognita or terra ignota (Latin "unknown land"; incognita is stressed on its second syllable in Latin, but with variation in pronunciation in English) is a term used in cartography for regions that have not been mapped or documented. The expression is believed to be first seen in Ptolemy's Geography c. 150. The term was reintroduced in the 15th century from the rediscovery of Ptolemy's work during the Age of Discovery. The equivalent on French maps would be terres inconnues (plural form), and some English maps may show Parts Unknown. Similarly, uncharted or unknown seas would be labeled mare incognitum, Latin for "unknown sea".
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Terra incognita in the context of Ancient world map
The earliest known world maps date to classical antiquity, the oldest examples of the 6th to 5th centuries BCE still based on the flat Earth paradigm. World maps assuming a spherical Earth first appear in the Hellenistic period. The developments of Greek geography during this time, notably by Eratosthenes and Posidonius culminated in the Roman era, with Ptolemy's world map (2nd century CE), which would remain authoritative throughout the Middle Ages. Since Ptolemy, knowledge of the approximate size of the Earth allowed cartographers to estimate the extent of their geographical knowledge, and to indicate parts of the planet known to exist but not yet explored as terra incognita.
With the Age of Discovery, during the 15th to 18th centuries, world maps became increasingly accurate; exploration of Antarctica, Australia, and the interior of Africa by western mapmakers was left to the 19th and early 20th century.
Terra incognita in the context of Cape Delgado
Cape Delgado (Portuguese: Cabo Delgado) is a coastal promontory south of Mozambique's border with Tanzania. It is the arc-shaped delta of the Rovuma River and was created from sediment deposited by the Rovuma as it empties into the Indian Ocean. It is sometimes identified with Prasum, the southernmost point of Africa known to the Roman geographers Marinus of Tyre and Ptolemy. In Ptolemy's Geography, it marked the point where Africa turned eastward along a great unknown shore to meet southeast Asia and enclose the Indian Ocean. Medieval Islamic cartographers dispensed with the idea at least as early as the 9th-century al-Khwārizmī but the conception returned to Europe following Jacobus Angelus's c. 1406 Latin translation of Maximus Planudes's restored Ptolemaic text and was not (openly) dispensed with until after Bartholomew Dias's successful circumnavigation of Africa in 1488.
Cape Delgado gives its name to Cabo Delgado Province of Mozambique.