Although in Harry Potter Canon this effect is a magical one, there are many canon places that may be considered unplottable.
- The Isla de Muerta from Pirates of the Caribbean. It can only be found by those who already know where it is.
- The Lost Woods from Legend of Zelda. Unless one is a forest creature or spirit, one will always become lost without a proper guide.
- The Labyrinth from Labyrinth. It is always changing and may not have been built with standard comprehension in mind.
- The Dark Island from The Chronicles of Narnia. It is a semi-gaseous dark area in the ocean that causes those who enter to see dreams... and often go mad from them.
- Mira from Baten Kaitos. It is a continent that constantly is floating in between and in and out of dimensions.
- The Maw from Star Wars Extended Universe canon. It is a cluster of unstable and unnavigable black holes, although people have found their way through it and there may be safe paths.
- Emyn Muil might be unplottable.
Places that follow non-euclidean or alien geometry are famously unplottable, as are places that actually change or even move around of their own accord.
PPC Headquarters is for all intents and purposes unplottable. If some sort of map exists, it would be in the hands of Flowers and no technology the PPC (or any discovered canon) has would be able to produce a copy. It passes through six dimensions, and the interior is famously impossible to navigate.
Somehow producing a map to or of these locations is a charge, and once the badfic is over the map will become completely useless.