For history professor Alan MacEachern, the idea came from leafing through a book from the 1940s about a woman who rode across Canada on horseback.

P.E.I. was not included on the map of Canada on the cover.

"I realized that must have been one of those times that P.E.I. floated out into the Atlantic," said MacEachern, who teaches at the University of Western Ontario but grew up on the Island.

"I thought it would be worth, as a historian, to study all those times when that happened in the past."

There have been recent stories of P.E.I. being left off the map, and the idea intrigued MacEachern. Just how common was it?

Finding the answer was a challenge, he said.

"You can't Google Prince Edward Island, because Prince Edward Island isn't there," he said.

But as it turns out, leaving P.E.I. off maps has been a habit of cartographers and illustrators that goes back centuries. The exhibit MacEachern put together includes not just maps, but illustrations for advertising, an original copy of a book of Champlain's voyages dating back to 1613, and a T-shirt that his daughter found.

The exhibit, Missing the Island, goes up at the end of May at the Confederation Centre Art Gallery, and will remain up until October.