Item from harry-potter-order-of-the-phoenix by
A magical map of Hogwarts that shows every person, every passage, and every secret room in the castle -- created by Harry's father and his friends, and essential this year for avoiding Umbridge's patrols.
The Marauder's Map was created by Moony, Wormtail, Padfoot, and Prongs -- Remus Lupin, Peter Pettigrew, Sirius Black, and James Potter -- during their school years, using their combined knowledge of the castle. Fred and George nicked it from Filch's confiscated items in their first year and gave it to Harry in his third. This year the Map is invaluable for DA logistics -- checking that corridors are clear before meetings, watching for Umbridge's movements, tracking the Inquisitorial Squad. It also shows something Harry noticed last year: people on the Map are never who you expect them to be. Barty Crouch Jr. appeared on the Map as himself, not as Moody. The Map doesn't lie and can't be fooled. The map shows Hogwarts as its creators knew it -- every joke, every secret, every passage the Marauders discovered in seven years of dedicated troublemaking. It is the most useful artifact in the series and the most loving portrait of Hogwarts ever made.
A large, folded piece of old parchment that appears blank. When activated by the phrase 'I solemnly swear that I am up to no good,' it reveals a detailed map of Hogwarts showing every corridor, room, secret passage, and -- crucially -- every person in the castle, represented by a labeled dot moving in real time. Cleared by the phrase 'Mischief managed.'
Also known as: the Marauder's Map, Marauder's Map, the Map