“Well, you can enchant a building so it’s impossible to plot on a map, can’t you?”
-- Hermione Granger, who has read Hogwarts, A History (GF11)
Unplottable is a term which is used to describe a magical effect on a place which makes it impossible for Wizards or Muggles to plot its location on a map (GF11), or even to find it if they go looking (OP6).
References from the canon
- Hermione suggested that this may have been done to make Durmstrang and Beauxbatons harder to locate by other witches and wizards (GF11).
- Hogwarts also has wards and spells on it to hide its true nature from Muggles, but it is apparently not Unplottable.
- The Room of Requirement is Unplottable, so that it doesn't appear on the Marauder's Map (HBP21).
- Number twelve Grimmauld Place is Unplottable (OP6).
- The Ministry of Magic in Burkina Faso has designated certain forests unplottable as Runespoor reservations (FB).
- Queerditch Marsh, the birthplace of Quidditch in the 11th Century, has been made Unplottable (RC).
Commentary
Notes
Rowling noted that witches and wizards can actually make themselves untraceable:
Just as wizards can make buildings unplottable, they can also make themselves untraceable. Voldemort would have been found long ago if it had been as simple as sending him an owl! (JKR)
Many fans believe that Hogwarts is Unplottable, and it may be. However, there is no evidence in canon to support that. The passage usually cited is this:
“There’s traditionally been a lot of rivalry between all the magic schools. Durmstrang and Beauxbatons like to conceal their whereabouts so nobody can steal their secrets,” said Hermione matter-of-factly.
“Come off it,” said Ron, starting to laugh. “Durmstrang’s got to be about the same size as Hogwarts -- how are you going to hide a great big castle?”
“But Hogwarts is hidden,” said Hermione, in surprise. “Everyone knows that.. . well, everyone who’s read Hogwarts, A History, anyway.”
“Just you, then,” said Ron. “So go on - how d’you hide a place like Hogwarts?”
“It’s bewitched,” said Hermione. “If a Muggle looks at it, all they see is a moldering old ruin with a sign over the entrance saying DANGER, DO NOT ENTER, UNSAFE.”
“So Durmstrang’ll just look like a ruin to an outsider too?”
“Maybe,” said Hermione, shrugging, “or it might have Muggle-repelling charms on it, like the World Cup stadium. And to keep foreign wizards from finding it, they’ll have made it Unplottable -“
“Come again?”
“Well, you can enchant a building so it’s impossible to plot on a map, can’t you?”
“Er. . . if you say so,” said Harry. (GF11)
The passage doesn't actually say anything about Hogwarts being Unplottable. It only refers to the other schools. The fact that Muggles would actually find a castle, albeit in ruins, suggests that it's not Unplottable, since Grimmauld Place's Unplottable status means that "Muggles could never come and call" (OP6).
