“Don’t trust the maps” was good advice for much of human history. The book The Un-Discovered Islands: An Archipelago of Myths and Mysteries, Phantoms and Fakes by Malachy Tallack, illustrated by Katie Scott, makes this point vividly by revealing the stories behind lands that weren’t really there.
For example, the 1783 Treaty of Paris that established the U.S.’s borders after the Revolutionary War stated the northern boundary passed “through Lake Superior northward of the Isles Royal and Phelipeaux.” But when surveyors went out in the 1820s they discovered Isle Phelipeaux was pure fiction.
The list goes on: some islands were invented to reinforce claims of accomplishment, others were thought to exist but later sank, and then there were the expected claims of fraud. Such is human nature.
The book is available on Amazon at https://www.amazon.com/Discovered-Islands-Archipelago-Mysteries-Phantoms/dp/1250148448/ref=sr_1_5?.
Taken from “Ancient Maps Show Islands That Don’t Really Exist” by Greg Miller (https://www.nationalgeographic.com/culture/article/maps-undiscovered-fake-islands-cartography?).