HOW COULD YOU MAKE YOUR OWN MARAUDER’S MAP TO SKIP CLASS?

Picture yourself on a wet Wednesday afternoon. You’re trapped in double business studies, the most tedious topic known to any school syllabus. No need to panic. A cunning plan is afoot. And it involves a magic map. Outside your tutorial of torture lies a Byzantine network of classrooms and corridors. Your mission, should you choose to accept it, is to negotiate this Kafkaesque chaos and escape into the life-giving sunshine, beyond the school sentries and boundary surveillance. But wait, what exactly does this magic map do?

In the Harry Potter Universe, such a magical document was known as the Marauder’s Map. With this map, the intricate layout of the sometimes subterranean, seven-storied, one-hundred-and-forty-two staircased, towered, turreted, and deep-dungeoned architecture of Hogwarts School of Witchcraft and Wizardry was clearly conjured up.

The map was an all-seeing eye into the medieval castle’s deep, dark heart. The map spied each and every classroom, all hallways, and every creepy castle corner. The castle grounds also fell under the map’s purview, as well as all the clandestine corridors hidden within its walls. Nor did witches and wizards escape its knowing reach. Each one was signified on the map by an animated set of footprints and a scroll-like caption. The Marauder’s Map was not fooled by Harry’s invisibility cloak, Animagi, or Polyjuice Potions. Even the Hogwarts ghosts were captured by its gaze.

True, the map was not infallible. It could not distinguish wizards or witches bearing the same name, for example. Neither does the map show unplottable rooms. The Room of Requirement, for example, was revealed by Dobby the house elf, and not the map itself, which seemed not to even know the Room existed. And the same was true of the Chamber of Secrets. It never appeared on the map. As with the Room of Requirement, the Chamber may not have been shown simply because the map’s creators, Remus Lupin, Peter Pettigrew, Sirius Black, and James Potter—also known as Messrs Moony, Wormtail, Padfoot, and Prongs, “Purveyors of Aids to Magical Mischief-Makers” —simply never knew of its existence. So, what would we need to make a muggle version of the Marauder’s Map?

Medieval Map Makers

Like Hogwarts itself, the golden age of map making was medieval, and it began with ships. Two Chinese inventions, the compass and the sternpost rudder, had a global effect at sea. Long voyages became viable. The seas were thrown open to exploration, piracy, a colossal expansion in trade, and war. The need for better navigation had profound consequences for map making. An open ocean meant more accuracy: better observations, better instruments, and better maps. So open-sea navigation raised the need for a brand new quantitative geography, and the desire for devices that could be used onboard ships, as well as on land. And so the obsession with longitude began.

The great European sea voyages started around 1415, and opened up the planet to plunder. The voyages were the fruit of the first conscious use of geography in the pay of glory and profit. Fledging empires soon realized they were able to exert global control based on knowledge of territory: knowing where you were and knowing what you owned. And so, navigation and mapping became even more important to trade. But the golden age of maps led to a golden age of piracy.

The pirates that preyed upon the high seas, an echo of rival trade and colonization attempts by European powers, often sought a surprising booty. If a sea raid proved successful, the boarding pirates would head straight for the hold. Rather than gold, silver, or pieces of eight, the most precious cargo a ship possessed was its maps and chronometer. Indeed, some cartographers would knowingly include errors on their maps, to mislead the uninitiated should the map get into the hands of the wrong kind of pirate.

Such cyphered anti-pirate maps bear a resemblance to the Marauder’s Map. The Marauder’s Map was also coded, normally disguised as a blank piece of parchment. To view the map, a wizard or witch had to tap it with their wand and say, “I solemnly swear that I am up to no good.” Only then did the map reveal itself. Similarly, to once more hide the contents of the map so the parchment again appeared blank, a wizard would tap it and say, “Mischief managed.” The only difference was this. Medieval maps were meant to guard against mischief, but the Marauder’s Map was designed specifically to cause it!

Tagging Teacher

A muggle version of the Marauder’s Map might be based on GPS. GPS, or the Global Positioning System, is a network of around thirty satellites, which orbit the Earth at a height of 20,000 kilometers. As with much technology before and after it, the system was developed for the military, the US military in this particular case. But eventually, anyone with a GPS device was allowed to use it. That’s whether you have a mobile phone or a plain GPS unit and can receive the radio signals, which are broadcast by the satellites.

No matter where you are on Earth, GPS will find you. Wherever you may roam, at least four GPS satellites are visible. Each of the satellites transmits data about where it is, and when it is. These data signals, beaming down at the speed of light, are picked up by your GPS. Once such data is done for at least three satellites, your GPS knows where you are. Your GPS receiver does this by a process known as trilateration. Now, imagine applying the technique to a school escape situation. Imagine a teacher is lurking somewhere within the school catacombs. High in the sky above sit the beady eyes of three satellites. Let’s call them satellites A, B, and C. If the lurking teacher is spied by satellite A, then that satellite will know just how far away he is. And if satellites B and C also spy the teacher, they too will read his position. So, taking all three readings together, where they intersect is the exact spot of the lurking teacher. And the more satellites there are above the horizon, the more exact will be the reading of the teacher’s position. All of this is done with a little help from Einstein.

To ensure the very best in time accuracy, GPS satellites carry atomic clocks. Einstein’s theories of Special and General Relativity predicted that an atomic clock in Earth’s orbit would show a slightly different time to an identical clock down on Earth. Einstein’s brilliant brain realized that time runs slower under a stronger gravity. So, the clocks on board the satellites will seem to run faster than their Earth-bound counterparts.

The satellites must make a correction for speed, as well as gravity. Each satellite in the GPS constellation orbits at a height of around 20,000 kilometers. And at that altitude, they speed along at about 14,000 kilometers every hour (that’s an orbital time of roughly 12 hours—contrary to popular belief, GPS satellites are not in geosynchronous or geostationary orbits). And as they travel at such speed, Einstein’s Special Relativity predicts the satellites’ clocks will appear to run more slowly than a clock on Earth! So, the whole GPS network must make allowances for these relativistic effects of gravity and speed on time.

Yet none of this should worry our potential escapee because the tech for tagging teacher is already with us. GPS security tags, used for tracking pets, people, or even prying teachers, are already on the market, are tiny, and are solar-powered. They are accurate to the meter, and work indoors. Using a super sensitive patch antenna, and being smaller than two flat AA batteries, these GPS security tags use a GPS satellite constellation. And all this means that, armed with a smartphone, a school escapee can easily plot current and previous positions of teachers simply by using a mapping app. So remains one last challenge: actually getting the tag onto teacher …