Through seven novels, readers got to know the Wizarding World fairly well, learning about the most important events in its history, its most notable wizards and witches (both good and bad), and some of its most fascinating charms and objects, of which many made it to the movie saga. One of, if not the most popular object in the Harry Potter universe is the Marauder’s Map, introduced in Harry Potter and the Prisoner of Azkaban when Harry couldn’t join the rest on their trip to Hogsmeade, so Fred and George Weasley, who were in possession of the map, gave it to him so he could use one of Hogwarts’ secret passages that would lead him to Hogsmeade.
The Marauder’s Map was created by Remus Lupin (who went by the nickname Moony), Peter Pettigrew (Wormtail), Sirius Black (Padfoot), and James Potter (Prongs) when they were students at Hogwarts. The map shows every classroom, hallway, corner, and even the secret passages of Hogwarts and everyone in it, represented by a dot with their names, and it couldn’t be fooled by animagi (as seen with Pettigrew in Prisoner of Azkaban), Polyjuice Potions, or invisibility cloaks. Creating such an interesting and even dangerous map wasn’t easy, and it took the group years to finish it. However, a big question about the Marauder’s Map remains: how does it work?
In order for the map to be able to track every single person in Hogwarts, including the ghosts, the Marauders used the Homonculous Charm, which once its cast onto a map, enables its possessor to track the movements of every person in the mapped area, and it's a strong enough charm to not be fooled by the aforementioned potions, cloaks, and more. Now, when it comes to how the Marauders knew every inch of Hogwarts so well, it was the result of teamwork: Sirius, Peter, and James’ animagi abilities enabled them to explore the castle grounds by night undetected, while the interior of the castle was mapped over time with the help of the invisibility cloak, which belonged to James at the time. In addition to the Homonculous Charm, the Marauder’s Map also had a special charm so it could repel and insult Severus Snape if he ever attempted to use it, as happened in Prisoner of Azkaban. Of course, the Marauder’s Map wasn’t perfect, and it couldn’t differentiate people with matching names and didn’t show unplottable rooms, such as the Room of Requirement.
As interesting as the Homonculous Charm sounds, it’s one of those many charms from the Harry Potter universe that haven’t been properly explored, and there’s little information about it. As for the Marauder’s Map, it will continue to be one of the most popular and fascinating objects from the Wizarding World and one with an interesting story behind it, as it shows how advanced the magic of the group was, and it’s a shame that their talents were overlooked for so long.