For most of the Christian centuries -- until the 14th -- maps of the world were commonly centered on Jerusalem and those parts of the globe of which the cartographers had no knowledge were filled in willy-nilly as their imaginations ran riot, often with totally fictitious lands, monsters and aberrations of every sort.
It has been suggested that the Catalan Atlas of 1375 was the first European cartographic production to omit what it did not know. As Daniel Boorstin has written: "In an impressive feat of self-control, the cartographer actually left parts of the earth blank."
Old traditions die hard, and the admission of ignorance is a rare human virtue. Imaginary lands -- such as a supposed great southern continent -- endured on some European maps right up to the time of Captain Cook.
Eventually the spirit of the Catalan Atlas prevailed, at least within the scientific community, and no cartographer today would dream of adding to a map of this world or any other what has not been confirmed to exist.
The courage to leave blank. To have unanswered questions. To say "I don't know." This, I would suggest, is the grandest achievement of the European Scientific Revolution.
It is not, of course, even today, a prevailing view. Most folks still fill in their conceptual maps of the world with imaginary constructs, most commonly that portmanteau "answer" to every unanswered question, God.
Some of us are content to live with the blank spaces on the map.
What came before the Big Bang? I don't know.
Why are the laws of nature what they are? I don't know.
How did life begin? I don't know.
How does a fertilized egg reliably develop into a human baby? I don't know.
What is the nature of consciousness? I don't know.
Big questions. Whole continents of knowledge waiting to be explored -- and, possibly, eventually mapped. In the meantime, we leave aside the fictional constructs that give an illusion of knowledge.