“Anyway, the Amakusa specialise in hiding and escaping. After stealing The Book of the Law and kidnapping Orsola Aquinas, they’ll expect the Roman Catholic Church to hit back full force. If this was a planned operation, then they might have rehearsed this part.”

Agnese, who was still clinging onto Index, looked puzzled as she said,

“But…but even then, no matter what, they can’t possibly escape our perimeter…”

“It’s possible. There’s a type of magic for that.”

Index replied without hesitation. At that, Agnese sucked in a deep breath.

“There's a spell that can only be used in Japan. Basically speaking, there are special places called ‘portals’ all over Japan. One can use this ‘map magic’ to travel from ‘portal’ to ‘portal’.”

[...]

“Ino Tadataka used the Idol Theory in the opposite manner. He understood that the real one and the idol would affect each other, so he plotted 47 ‘portals’ on the Dai Nihon Enkai Yochi Zenzu that originally didn’t exist on the Japanese islands. Thus, these entrances that allow people to come and go as they please appeared in modern Japan.”

The Japanese islands and the intricate map of Japan that the guy called Ino Tadataka had made could actually affect each other. Once one randomly drew a teleportation entrance on that map, such an entrance would appear on that real island as well.

Toaru Majutsu no Index vol.7 ch.2 pt.2