harry potter - Is it possible to hide from the Marauders Map?

I am trying to explain to myself why Peter was not caught in the same bed as Ron, and I now wonder whether there is anyway to trick the map.

Is it possible to hide from the Marauders Map?

Answer

Not as far as we know ...

From the Pottermore fact file on the Marauders' Map:

Shows the location of any person or ghost on Hogwart’s grounds, isn’t fooled by an Animagus or an Invisibility Cloak

As far as I can remember, there's no case in canon of anyone ever managing to hide from the map. It detected Peter Pettigrew when he was in rat form; it detected Barty Crouch Jr. when he was using Polyjuice Potion; it detected Harry Potter when he was under the Invisibility Cloak. If there's any concealing magic sufficiently powerful to bamboozle it, we never saw it in the books.

As for why Peter Pettigrew was never seen in the same bed as Ron, the simple solution is that among so many people in the castle, nobody noticed. The best way to avoid being detected using the Marauders' Map is simply to hope that the user of the map doesn't notice you. See also Why couldn't Harry or anybody else see Peter Pettigrew aka Scabbers on the Marauder's Map when Lupin could?, where the top answer has a quote from JKR as follows:

Why didn't Fred and George notice Peter Pettigrew on the Marauder's Map before ("Prisoner of Azkaban")?

It would not have mattered if they had. Unless somebody was very familiar with the story of Sirius Black (and after all, Sirius was not Mr. and Mrs. Weasley's best friend – indeed, they never knew him until after he escaped from Azkaban), 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.

... unless you go to the right place.

Although we never see any concealing magic which can fool the map, it's possible not to appear on it simply by being in a location which it doesn't cover. For instance, leaving Hogwarts (a trivial solution, since the map is a map of Hogwarts alone), or going to the Room of Requirement (apparently the magic which makes the Room undiscoverable is stronger than the magic which makes the map plot everything). As discussed in the top answer to Why didn't the Marauder's Map show Mad Eye Moody hidden in the trunk?, it's definitely true that the Room of Requirement doesn't show up on the map:

Although he consulted the map as often as he could, sometimes making unnecessary visits to the bathroom between lessons to search it, he did not once see Malfoy anywhere suspicious...at these times Malfoy was not only nowhere near them, but impossible to locate on the map at all. [...] And still there were those inexplicable times when Malfoy simply vanished from the map [...]

“I think it’ll be part of the magic of the room,” said Hermione. “If you need it to be Unplottable, it will be.”

_{-- HP and the Half-Blood Prince}