When designing the "Harry Potter" universe on screen, everything had to be consistent. It's an elaborate world, and just one slip could ruin the magic.
But there was one major problem the filmmakers faced over and over again: the series wasn't finished.
Half of the "Harry Potter" movies were made before J.K. Rowling finished the books. So when some things were introduced early in the story, it wasn't clear how they'd be important later on.
One complicated prop in particular needed to reveal a lot more: The Marauder's Map. It's a magical map of Hogwarts' grounds that reveals the location of everyone on it.
The Map first appears in Harry's third year at Hogwarts. In "Harry Potter and the Prisoner of Azkaban," Harry uses it to discover Peter Pettigrew, the man who betrayed the location of his parents to Lord Voldemort. But it's useful, and Harry ends up using it in his later years at Hogwarts.
Miraphora Mina, co-founder of the graphic design firm MinaLima, was one of the three people who designed everything in the "Harry Potter" movies. She didn't anticipate the scope of the map's importance after "Prisoner of Azkaban," or how to show parts of Hogwarts that weren't known be known in earlier films.
She solved the problem by making it a little more magical.
"The thing is, it’s designed in such a way where when you unfold it, it’s a mystery," Lina said. "You don’t quite know what layer you’re on. It’s like a scroll. And so we were able to keep adding new layers of map, and layers of school, into the design of it."
As the films progressed, she added new things to different layers of the map. The map was based on the architectural drawings of Hogwarts made by Stuart Craig. Because it's it's enormous, it's folded up to become portable.
Here's what the map looked like in "Harry Potter and the Prisoner of Azkaban," at the 47 second mark:
With each subsequent movie, different parts of the folded map were revealed, with previously unknown parts of Hogwarts added on. In "Harry Potter and the Half-Blood Prince," for example, MinaLima added a corridor on the seventh floor.
It was also tricky because the map itself had such a complicated design. It was made by Harry's father, James Potter, and his friends Sirius Black, Peter Pettigrew, and Remus Lupin while they were themselves students at Hogwarts a couple of decades earlier. Mina dug into their characters to design the map, rather than making it look like a treasure map or something more generic. Having flickering, animated, and handwritten lettering helped.
"We knew they were smart kids with a lot of cunning and craftiness, and with very good imaginations," she said. "So we came up with something that was sort of whimsical, but it also had a sort of intelligence, which is why we wanted to have all the words."
There are other objects throughout the "Harry Potter" series that turn out to have later significance. The most prominent example is Tom Riddle's diary in "Harry Potter and the Chamber of Secrets." In the sixth book, we learn it turned out by the to be a horcrux, an object housing a fragment of Voldemort's soul.
But there are few objects as complicated as the Marauder's Map that had to appear so much onscreen. And every movie revealed a new layer of its design.
