The map is not fooled by Polyjuice potions, Animagi, invisibility cloaks, etc. Why is there not widespread use of maps like these for identification/security purposes?

We know it is possible to infiltrate, for instance, the Ministry of Magic using these methods. However, a map of the Ministry (or at least the entrance) would give a guard perfect information about who is coming in and out, rendering most obvious disguises useless.

Another one is, when the snatchers (or Death Eaters) were hunting the trio, why not enchant a map of a given area to see if someone with their name was there? Even if they will search the area anyway, it would help verify anyone they catch is who they say they are.

I initially thought the Marauder's Map was unique to Hogwarts, but I recently read it was was created using a Homonculous Charm (see here and here) The spell does not sound particularly unique, so I get the impression it can be cast on arbitrary maps. I've been reading other answers to similar questions, and while everyone agrees it was very clever (even genius) magic, nobody says the spell cannot be cast on arbitrary maps.

Anyway, it sounds it could be used as a standard method for identification (at least passing the Marauder's Map test could be a minimum requirement). Why is that not the case?

I'll agree it is a given that the spell is hard, and thus most would not bother with it. Also, as pointed out, since it is primarily a tracking it is probably not considered when planning security/identification. And if it was, I think the conclusion that most people would object to something so invasive is reasonable.

I still think there is a lot of room for using and abusing the map. Are there radar/tracking tools more powerful than something which can accurately track and label everyone in a given area, regardless of disguise? It probably has limits, but it doesn't appear that way from the books. I think the Marauder's Map is not unique, but I'll accept the answer below as to why its use is not commonplace.

  • Two reasons: Since this was mostly a child's toy, I suspect there were likely far more sophisticated tools in place depending on the need (though no one seemed to think about using one, so there must be inherent limitations. Perhaps you can't track adult wizards, unless they allow it). Honestly, I think it was one of those things created for the story without much consideration for what a technology might mean in a wider setting. Commented Sep 20, 2013 at 20:04
  • But a children't toy that isn't fooled by methods used to infiltrate the Ministry? It's probably reasonable to conclude there must be inherent limitations, but what are they?
    – Mauricio
    Commented Sep 20, 2013 at 20:28
  • 7
    @Thaddeus Harry used it to track Pettigrew and Snape, so I don't think there's an "adult wizard" limitation. Pettigrew wouldn't wanted to be tracked, and Snape didn't know about it (so it wouldn't be opt-in or opt-out)
    – Izkata
    Commented Sep 20, 2013 at 23:25
  • 1
    Non-canon, but I would theorize that the map makes use of Hogwart's unique magical ambience. Commented Aug 8, 2014 at 21:56

4 Answers 4


Mostly theorizing here, based on what I remember from the books and the other comments and answers. A main reason why such a map could not be used in lots of places, I think, is the effort needed to enforce such a map. I will get back to this point.
Let's take the Ministry as an example
I think the point is not about being able to increase the security by tracking people with their true identities, but about whether anyone would like to be tracked that way or not
The Ministry had officials upto the level of the Minister of magic, and I am sure many of them would likely complain to the idea of being tracked continuously through out the Ministry. That is why they have tighter security at the entrances. For instance, there are guards with secrecy sensors, which are probably considered more robust magic specially catered to security (compared to Homunculus charm). In fact, using Homunculus charm to track people might not be considered a security measure at all, when more advanced magic specially built for security is available. So in fact, there might even be restrictions inside the Ministry so that people Cannot be tracked using this method. Such restrictions may not be present at Hogwarts, because, although Hogwarts is secure, it's still a school, and not a government building like the Ministry. It is likely Hogwarts never thought about the ability to track people within the school grounds as a potential security risk. Making a map like that also probably requires a lot of time and effort, and the fact that children at school might be able to pull something like that off probably didn't cross anyone's mind (eg: students weren't allowed to be outside after dark; the map creators could move around only because they could turn into animals)

For this same reason, I don't think snatchers would have something similar to the map as a tool. They seem to be random gang of thugs who want to make quick money by turning in muggle borns, and probably they keep on moving from place to place. They would not want to spend the effort needed to make such a map for all the places that they visit. The Ministry most probably did not endorse them officially and so could not provide any kind of tools.

As for the Death Eater Ministry officials who might go out hunting for muggle borns (like the people who were sent to Lovegood's house), the effort needed to make such maps would imply that it's not practically feasible to make a map of every place that they have to go to, and also since they have more powerful security and identification tools at their disposal, this method as a security measure would not cross their minds

  • I'm leaning towards this answer...maybe there IS a hard counter, like you say. I mean, it's not entirely satisfying because the "more robust methods" failed against the invisibility cloak and the polyjuice potion, where the map succeeded. I'm not really seeing how there are "better" alternatives unless the map's magic can be disabled altogether. I agree its widespread use would be met with opposition, since it's very invasive, but tracking you through an entrance hardly equates to tracking your every move.
    – Mauricio
    Commented Sep 22, 2013 at 3:05
  • Tracking you through just the entrance may be a good idea, but like I said, officials inside the Ministry may oppose to being tracked at all, which is why there might be arrangements inside the Ministry so that tracking of people inside the building cannot be done. Hence there would be more guards at the entrances with more specialized equipment of security and identification, so the use of homunculus charm as a security measure would not be considered. Moreover, someone under the invisibility cloak or polyjuice potion would probably not be able to get past a guards check post at the entrance
    – user13267
    Commented Sep 22, 2013 at 4:37
  • if they were being personally checked
    – user13267
    Commented Sep 22, 2013 at 4:37

I believe that part of the reason why the map worked so well is secrecy. Very few people knew that the map has existed, which is why few have tried to deliberately hide themselves from the map.

In Deathly Hallows, trackers might have used enchanted maps and other spells to find wizards in hide, but Hermione has specifically cast protective spells to various ways they could be found, and one of these might have hidden them from enchanted maps.

This doesn't really explain the Ministry infiltration, because it doesn't seem like the trio has used any spells to avoid being detected by a map. Perhaps some earlier preparation, such as a long-lasting spell or magic item, has shielded them at that time.

As an out-of-universe example, the Order of the Stick webcomics features an epic spell that shields an entire city from tracking people in it by magical divination, and this spell still protects from tracking people who leave the city for a few weeks after they leave.

  • That's a good point. It would be very like Hermione to cast something as overkill as cloister from OOTS (she's probably epic-level anyway) and that would help explain the Ministry infiltration. But I don't know how obscure the map's magic is, since it wound up at the reach of schoolboys (yet again, this is the same school where another teen unleashed a Basilisk, so who knows).
    – Mauricio
    Commented Sep 24, 2013 at 4:07

Pottermore merely states that Homonculous Charm was used to "track people". It doesn't explicitly say that it was used to label people with correct names.

"The magic used in the map's creation is advanced and impressive; it includes the Homonculous Charm, enabling the possessor of the map to track the movements of every person in the castle, and it was also enchanted to forever repel (as insultingly as possible) the curiosity of their nemesis, Severus Snape.

E.g. think Radar or motion detector vs. IFF or transponder or facial recognition in muggle technology.

  • So, are there other charms at work? The map tracks AND correctly labels people the original makers knew nothing of. If it was only for tracking you would have to know who you are tracking to label it. How did the map know?
    – Mauricio
    Commented Sep 20, 2013 at 21:26
  • @Mauricio - no canon info I'm aware of other than this. Commented Sep 21, 2013 at 0:15
  • Then the map works "somehow" in conjunction with the Homonculous Charm. Is there no information on why (whether) it's not replicable?
    – Mauricio
    Commented Sep 21, 2013 at 1:43

As a side note, I would like to add that the Ministry doesn't have such a high level of skill as many would think.

Really gifted wizards mostly become Aurors who work in the field, professors, researchers, alchemists, dark wizards or they don't work at all. While some of these still fall under the Ministry, the people who work inside the Ministry are quite average.

For example: the average Ministry worker wasn't able to cast a Patronus (otherwise guarding the interrogation room with dementors would be quite useless) and wasn't even able to use 'Finite Incantatem' to stop it from raining in their office (Yaxley).

Therefore I don't think these people would have the skill to produce such a map, if it were possible.

  • This answer would be greatly improved if you edited in some evidence to back it up.
    – TheLethalCarrot
    Commented Jan 4, 2019 at 10:01

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