What kind of beings are shown by the Marauder's Map?

Question

The map definitely shows people (humans) inside the castle, but I remember reading about Harry watching Peeves bouncing around in the trophy room and Peeves is not human. I don't remember if I had exactly read it or not, but the wiki page for the map says that it shows the ghosts as well.

What kind or creatures or beings come under the map's radar? Any living creature? Or humanoids? Or creatures with a significant size or intelligence? Would it show the house elves in the kitchen, centaurs in the forests and the merpeople in the lake as well? What about the giant squid and the thestrals or unicorns? Would it have shown the troll from the Philosopher's stone if they had the map then? What about Quirrell/Voldemort? Would he have shown up on the map? And the basilisk from the Chamber of Secrets (the book)? Maybe the chamber itself was unplottable but if the map could show the basilisk he would have been visible when he was slithering around in the pipes.

Answer 1

The Marauder's map showed humans (obviously), Peeves and the other ghosts, and transformed animagi, as well as Mrs. Norris and Crookshanks, but not insects or vermin (other than Pettigrew, of course; if it did show animals to that level, the map would be a complete mess and unreadable). It showed these beings from every inch of the Hogwarts castle and grounds. So it seems to be any living creature of a certain level of intelligence or higher.

The books never mentioned Dobby, Winky, or any of the other house-elves as appearing on the Map, and Harry never looks at it when any forest creatures are in the castle, but it seems (since cats and animagi can be seen) that it would in fact show the troll, as well as the thestrals and unicorns.

As for the Basilisk, it would probably show it when he was in the castle (though Riddle/Voldemort may have charmed him so as to be personally "unplottable"), though the squid probably does appear on the map (although was never mentioned). Interestingly, this means that the Beauxbatons Stagecoach and the Durmstrang Ship should also logically appear on the Marauder's Map when on the grounds.

EDIT: The map was, according to Rowling on Pottermore, made using a Homonculous charm. "Homunculus" is a word that refers to a (small) human or humanoid; so it wouldn't be much of a stretch to say that the map detects anything that is human or humanoid (that is, human-like if not specifically human-shaped).

Answer 2

Just re-read book 3. Mrs Norris is mentioned and the Animagi Peter and Sirius were mentioned. Crookshanks was not.

As far as Fred and George noticing "Lord Voldemort" in book 1, they probably would notice but then again, then never made mention of a man named Peter Pettigrew sleeping in Ron's bed for 2 years. Maybe they wouldn't notice Tom Riddle.

Answer 3

The Map shows all beings who might prevent mischief. Thus, Peeves and Mrs Norris are shown and Crookshanks is not.

The Maurader's Map was designed to aid mischief:

Messrs. Moony, Wormtail, Padfoot, and Prongs Purveyors of Aids to Magical Mischief-Makers are proud to present THE MARAUDER’S MAP.

Also:

He took out his wand, touched the parchment lightly, and said, “I solemnly swear that I am up to no good.”

Also

“I’m getting there, Sirius, I’m getting there… well, highly exciting possibilities were open to us now that we could all transform. Soon we were leaving the Shrieking Shack and roaming the school grounds and the village by night. Sirius and James transformed into such large animals, they were able to keep a werewolf in check. I doubt whether any Hogwarts students ever found out more about the Hogwarts grounds and Hogsmeade than we did… And that’s how we came to write the Marauder’s Map, and sign it with our nicknames. Sirius is Padfoot. Peter is Wormtail. James was Prongs.”

These quotes show us that the map was intended for mischief, and specifically, was invented for James and Co. to be able to sneak around camp grounds.

Mrs Norris was trained to prevent mischief:

Filch owned a cat called Mrs. Norris, a scrawny, dust-colored creature with bulging, lamp like eyes just like Filch's. She patrolled the corridors alone. Break a rule in front of her, put just one toe out of line, and she'd whisk off for Filch, who'd appear, wheezing, two seconds later.

Thus the Maurader's map showed Mrs Norris.

It would presumably also show other beings that would disrupt mischief.