In one of the Harry Potter books (films), Harry gets a magic map of Hogwarts that shows the location of every person there. Has anyone made a similar spell or item that works within the Ars Magica rules?
Much harder in Ars Magica, though I do suppose a map of a very limited are, using T: Structure could be done.
I shall have to poner this deeply.
There is a magus in Magi of Hermes who has a map that is somewhat similar, IIRC.
I'll have to take a look in Magi of Hermes then.
The main issue I can see (with the T: Structure) map is the Warping it would cause.
EDIT:
The Map of Many Places (MoH, p. 104)? Not exactly the same thing, but useful.
That would be against the Code to spy on your fellow magi.
Legal technicalities.
I'm sure it could be made so that it would not detect anyone with a parma.
Besides, it's not spying unless you get caught.
Even ignoring the Code it breaks the current Magic Theory to have it function like the Marauders Map. Not only do you need to know and track all moving beings that are alive or dead within a structure but you must KNOW who each of them are. You would be casting InMe without seeing or having any AC to a target.
Target the structure and include an AC to that. There are items in both Legends and Projects (perhaps elsewhere) that function on an inserted AC. I don't see any reason at all why a fixed AC can't be enchanted.
Make it a duration concentration and usable a few times per day so folks in the structure don't suffer from long term warping. I've no books here but I suspect In Co to know the location of a body has got to base 1 or 2. I'd wager knowing the location of a mind to be not too much more difficult. So if you don't want names of folks I'm pretty sure that you can get by without causing powerful effect warping.
base level 1 (guess) +4 for AC, +1 for concentration, +3 for structure gets you level 25. Does powerful effect warping start at magnetude 6 or is my memory once again failing me?
If you want names (something like posing the silent question) or a target of structure +1, or I'm wrong about the base level, you can save three magnitudes by making it the effect range touch and placing it within the building. Then use a range AC device to recreate the image on the item in the building. (You still might not be able to pull off the names of the people in the structure without running into powerful effect warping I'm not sure what level the base for posing the silent question is).
3, actually.
In this regard, you are right. But the Base level is 3. However, there's no need for an Arcane Connection as long as the map works only within the Structure -- Touch is sufficient. This drops the level down to 20.
So we're at Base 3, +1 Conc, +1 Touch, +3 Structure
InCo 20.
tells you where everybody in a structure is, but not who they are.
Must presumably be touched to a wall or the floor to work.
Not bad really.
How about basing it off something like Sense the Feet that Tread the Earth?
Lemme take a half-hearted stab at it.
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Sense the Feet that Tread the Halls
InTe 49
R: Arc, D: Constant, T: Structure
Senses what is moving along the floor of the structure targeted by the included Arcane Connection.
(Base 4, +4 Arcane Connection, +2 Sun, +3 Structure, +1[sup]L[/sup] 2/day, +3[sup]L[/sup] Environmental Trigger)
Add Size modifiers and Penetration to taste.
Maybe this could be built as a magical sense effect?
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Show the Feet that Tread the Halls
CrIm 17
R: Pers., D: Constant, T: Individual
Creates a scale image of the the footsteps of what is sensed by the above effect.
(Base 1, +2 Sun, +2 Moving images, +1 Complex images, +1[sup]L[/sup] 2/day, +3[sup]L[/sup] Environmental Trigger, +3[sup]L[/sup] Linked Trigger)
But how do you know the names of all the people within the structure without ACs to them?
That requires a Mentem requisite, and penetration.