Item from harry-potter-deathly-hallows by
A magical parchment showing every person in Hogwarts in real time -- created by four friends, three of whom are dead and one a traitor. Harry keeps it. The Map remembers everyone.
The Marauder's Map sees through all disguises -- Animagus, Polyjuice, Invisibility Cloak. It shows the real name of every person in Hogwarts. During the Battle it would show every Death Eater, every student, every defender. It is the most complete intelligence asset in the castle, created by teenagers who wanted to sneak to the kitchens and accidentally built a masterpiece of surveillance magic.
Worn parchment that reveals a complete, real-time map of Hogwarts when activated with 'I solemnly swear that I am up to no good.' Tiny labeled dots show every person in the castle. 'Mischief managed' wipes it blank.
Also known as: the Marauder's Map, Marauder's Map, the Map