As the film progresses and Kraft gradually comes to believe that the map controls him, the map on the wall becomes slightly larger in each progressive scene, symbolizing it slowly controlling him.
Stephen King says he was thinking about this film when he wrote his short story "Obit", about a young writer who discovers he can kill people by writing an obituary about them. The short story is in King's Bazaar of Bad Dreams collection. He references the film in the foreword to the short story.
When Bob Kraft (Richard Boone) waits for phone calls at his desk, on the wall behind him is a picture of John Wilkes Booth.