Dr. Helen Young, who universally goes by Nell, is a gifted cartographer who once had a promising career at the New York Public Library. After a bitter dispute with her father over a seemingly worthless map—an event known as the "Junk Box Incident"—she was exiled from her chosen field. She now investigates the mystery surrounding her father's recent death and the 1930s road map that originally ruined her career.

A specialist in contemporary cartography, Dr. Felix Kimble was also disgraced during the "Junk Box Incident" when he attempted to defend Nell. Unlike Nell, he has moved on and now works for the tech conglomerate Haberson Global, developing an ambitious digital map project. He is logical and hopes to rekindle his relationship with Nell while guiding her back to a prestigious career.

Daniel is one of the NYPL's most celebrated cartography scholars and Nell's father. Seven years ago, he fired his own daughter over a dispute regarding a box of old maps. His recent murder, combined with his secret retention of the very map that caused their estrangement, pushes Nell into a deep investigation of his hidden past.

Tamara, known as Tam, was a highly gifted cartographer, Daniel's wife, and Nell's mother. She tragically died saving baby Nell from a fire under mysterious circumstances. Her legacy lives on through the mysterious maps left behind and the stories told by her former university friends.

Wally is an introverted, logic-driven student who joined a group of talented cartography friends at the University of Wisconsin. He is deeply devoted to Tam, his childhood friend, though he struggles with her expanding social circle and romantic attachment to Daniel. He serves as the group's researcher and quiet observer.

Dr. William Haberson is the ambitious CEO of the tech conglomerate Haberson Global. He is singularly focused on developing the Haberson Map, a digital project he believes will be the perfect map capable of outperforming all major tech companies. He is a demanding leader who prioritizes control and technological omniscience.

Dr. Humphrey Turan is Nell's supportive boss at Classic Maps and Atlases. He recognizes that Nell is vastly overqualified for her job creating replica maps and continuously encourages her to pursue her dream of returning to the NYPL. He provides a stable, encouraging environment for her after her fall from grace.

Bear was one of the university students who joined Tam and Daniel's close-knit circle of cartographers. He helped research and map utilities for the group's ambitious Dreamer's Atlas project, working alongside his peers during their post-graduation summer in upstate New York.

Ramona, or Romi, is a secretive and shady maps dealer operating a hidden shop. She is deeply paranoid and reluctant to discuss her past, but she reveals that she, Daniel, and Tam were part of a tight-knit group of university friends called the Cartographers who attempted an ambitious mapping project decades ago.

Francis is a successful, influential figure in the map collecting world who authored a mysterious note found by Nell. Decades ago, he was a favored cartography student who dated Romi and worked on the Dreamer's Atlas project alongside Tam, Daniel, and the rest of their cohort.

Eve is an expert on Sanborn maps and a former member of the original Cartographers friend group. She holds vital memories of the summer the group spent in upstate New York and provides Nell with crucial context regarding the mysterious compass rose sigil and the group's historical dynamic.

Swann is an established figure at the NYPL Map Division and served as Nell's former mentor. He remains a steadfast, fatherly figure in her life even after her dismissal, continually supporting her ambitions and attempting to mediate between her and the police during the investigation into Daniel's murder.

Irene is the current chair of the New York Public Library. She is desperate to secure funding for the struggling institution and views Daniel's secret project as a potential lifeline. She offers Nell a chance to return to the library if Nell can uncover the details of her father's work.