Marauder’s Map

Notes

Rowling's comments about the map:

"The Marauder's Map subsequently became something of a bane to its true originator (me), because it allowed Harry a little too much freedom of information" (Pm)

While Harry did not give the Marauder's Map to any of his children, J.K. Rowling said his son James Sirius probably stole it from his desk in the grand tradition of his Marauder namesakes and the Weasley Twins (BLC)

Snape could not open the Marauder's Map, even using a revealing spell, and some fans believed it was because he was "up to good," trying to keep Harry from going to Hogsmeade because Sirius Black had escaped from Azkaban. But now we know that the Marauders, who saw Snape as their "nemesis," put a spell to "forever repel" him from seeing the Map (Pm).

The Marauder's Map also insulted Snape the first time he tried to read it. Interestingly, the first insult came from Remus Lupin, considered my many fans to be the "nicest" Marauder, and Harry's favorite teacher.

“Mr. Moony presents his compliments to Professor Snape, and begs him to keep his abnormally large nose out of other people's business.
Mr. Prongs agrees with Mr. Moony, and would like to add that Professor Snape is an ugly git.
Mr. Padfoot would like to register his astonishment that an idiot like that ever became a professor.
Mr. Wormtail bids Professor Snape good day, and advises him to wash his hair, the slimeball.”

But how did those insults come to be embedded in the Marauder's Map? Rowling explained that some objects allow wizarding "voices to be heard" even after death.

"... think of Bertha Jorkins rising out of the Pensieve in 'Goblet of Fire', the Sorting Hat continuing to spout the wisdom of the Founders hundreds of years after their deaths, the ghosts walking around Hogwarts, the portraits of dead headmasters and mistresses in Dumbledore's office, not to mention Mrs. Black's portrait in number twelve, Grimmauld Place... there are other examples, too, of which the Marauder's Map is merely one. It is not really Prongs writing the insult to Snape, it is as though he left a magical recording of his voice within the map" (JKR).

Inconsistency: Repelling spell or not, Snape was indeed able to see the Map when he discovered that Lupin had not taken his Wolfsbane Potion:

"You forgot to take your potion tonight, so I took a gobletful along. And very lucky I did... lucky for me, I mean. Lying on your desk was a certain map. One glance at it told me all I needed to know. I saw you running along this passageway and out of sight" (PA19)

It's true that Lupin did not have time to say "mischief managed" to close the map after he saw Sirius luring students to the Whomping Willow. This is still rather troublesome because the Map should have closed on its own without allowing Snape to see anything since the repelling spell was directed at him alone.

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Other inconsistencies:

The Weasley Twins never noticed that Professor Quirrell was always with someone named Tom Riddle (on the back of his head). Perhaps they did notice, but the name wasn't familiar to them, and certainly not synonymous with Lord Voldemort at that time. Harry did not have the Map in his first year, but he heard Quirrell talking to someone without seeing who it was, and even then the improbable truth never occurred to him (why would it?). Finally, the Twins just didn't care enough about Quirrell to pay any attention to him, which played right into Voldemort's hands.

However, the in Harry's second year, the Weasley Twins also never saw the Basilisk prowling around on the Marauder's Map. The Chamber itself could only be opened by a Parselmouth, so the Marauders wouldn't have known to put it on the Map (Pm). But once the Chamber was open again, the Basilisk could only leave through the pipes in Moaning Myrtle's bathroom and into the corridors which were shown on the Map. It's possible that either Slytherin or Tom Riddle had made the Basilisk itself unplottable except to a Parselmouth, but it's probably more likely the Weasley Twins never had the Map opened at the moment someone was petrified by the beast, which only took a few minutes of staring.

Finally, the biggest Marauder's Map question was how the Twins missed the fact that not one, but two of their brothers - Percy, then Ron - slept with a man named Peter Pettigrew every night, disguised as Scabbers the rat. It's understandable that the Twins might ignore "Big Head Boy" Percy when looking on the Map, but are we to believe they never checked up on Ron even during his first few months at Hogwarts? After three years they probably should have noticed.  Rowling did address this plot hole on her Official Site, although the answer may not satisfy everyone:

Fred and George would be unlikely to know or remember that Peter Pettigrew was the person Sirius had (supposedly) murdered. Even if Fred and George HAD heard the story at some point, why would they assume that the 'Peter Pettigrew' they occasionally saw moving around the map was, in fact, the man murdered years before?
Fred and George used the map for their own mischief-making, so they concentrated, naturally enough, on those portions of the map where they were planning their next misdeeds. And finally, you must not forget that hundreds of little dots are moving around this map at any given time… Fred and George did not know everyone in school by name, so a single unfamiliar name was unlikely to stand out.(JKR)

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The Ethics of the Marauder's Map

Having just been involved with Tom Riddle's Diary in his second year, Harry was a bit wary of the Marauder's Map. Right away he knew it could be dangerous:

"...even as he stood there, flooded with excitement, something Harry had once heard Mr. Weasley say came floating out of his memory. Never trust anything that can think for itself, if you can't see where it keeps its brain. This map was one of those dangerous magical objects Mr. Weasley had been warning against...." (PA10).

The Marauder's Map is magical equivalent to a network of surveillance cameras, which most people find invasive in modern society. So while there's no doubt the Map was ingenious and often great fun for sneaking around, it raises some ethical questions that were never addressed in the books. When is it appropriate for students to spy on people? Exactly what did the Marauders do with such information on a daily basis? If it was just about avoiding Filch or staying out of trouble with other teachers, that would be fine. However, if the Marauders used the Map to discover when certain students were alone and could be ambushed by the four of them against one - as we know the Marauders often did with Snape - then that seems to be an abuse of a magical object.

When Harry was lonely during the search for the Hallows and Horcruxes, he often opened the Map and watched his girlfriend Ginny's "dot" moving around at Hogwarts, of which Rowling says she approved (Pm). But one can imagine James using the Map the same way to spy on Lily and seeing her "dot" walking with Severus to the library or somewhere, becoming jealous, and plotting revenge (or letting Sirius plot it for him).

Years later, when Remus Lupin knew that Sirius Black was lurking around Hogwarts, he stayed true to his secretive Marauder roots and never gave the Map to Dumbledore, which led to his untimely transformation to a Werewolf on the same night that Peter fled back to Voldemort. In the fourth year, the Map fell into the hands of Death Eater Barty Crouch Jr./Fake Moody, who was able to use the Map with ease apparently, being always "up to no good."

The Map was a truly special magical object, but wasn't that useful for protecting the school, and in theory seems a little creepy.