ICELAND-FRISLAND. - CARTA DA NAVEGAR DE NICOLO ET ANTONIO ZENI FURONO IN TRAMONTANA LANO MCCCLXXX. . .

The discovery of America by the Venetian Zeni brothers in 1380, - before Columbus??
A large copper engraved map of the North Atlantic region, supposed after a middle age manuscript. Published in the "Annales de Voyages" ,by Malte-Brun, Paris
This interesting map of the North Atlantic is one of the most enduring cartographic mysteries. Known as the Zeno map, it first appeared in Venice in the year 1558 with an account of the exploits of Nicolo and Antonio Zeno into the region in 1380. The brothers allegedly traveled to Frisland (a fictitious island south of Iceland, perhaps the Faroe Islands) and the east coast of Greenland where they heard from the natives of the lands to the west called Estotiland (Labrador) and Drogia (Newfoundland).
The account was published by a Zeno ancestor purportedly from a surviving journal and manuscript map. It was probably created to give Venice, the author's native city, the credit for discovering America more than a century ahead of Columbus.

The map shows the North Atlantic and the countries bordering it, which the author claims is contemporary with the events recounted in the book. It is now known that the narrative was manufactured by the younger Zeno himself not long before the publication of the book, and the same is true of the map.
So it does in no way reflect geographical knowledge in the 14th century. We now know that Zeno's principal sources were Olaus Magnus' map of the North, the Caerte van Oostland of Cornelis Anthoniszoon, and old maps of the North of the Claudius Clavus type with elements taken from southern sea charts of the 15th and 16th centuries.
As for Zeno's Iceland, we need not look far to its sources, it is obviously taken from Carta Marina. The mountains, rivers and all the pictures are gone and the ice floes off the east coast on Olaus' map have become islands. In spite of its discreditable parentage, the Zeno map was to have a remarkable career. For the next 40 years it influenced most maps that were made of Iceland.
The narrative of the Zeno’s adventures was disputed at the time of publication and remained a source of controversy even into the 20th century. Even so, it was still taken seriously by many scholars and cartographers because it delineated certain features of the northern Atlantic regions that cannot be traced on earlier charts that have survived. The map was reproduced for Ruscelli's edition of Ptolemy, used as a source for Mercator's important world map of 1569, incorporated into Ortelius's 1570 map of the Arctic regions.
It was used by early English explorers in search of the Northwest Passage, and its errors in latitude are known to have deceived Frobisher. Thereafter story remained dormant for about a hundred years until it was revived by Forster and Buache in the late 18th century.
The Hakluyt Society published an English translation in 1873 and in 1883 Baron Nordenskiöld argued in favor of the validity of the narrative. Finally in 1898, Frederick Lucas concluded that it was a hoax after an extensive study in which he identified its main source to be Olaus Magnus' Carta Marina, along with other 15th and 16th century maps.

Reference: Burden #26.