The theme of obsession plays a large role in shaping the plot and character development in The Cartographers, most particularly in terms of Wally and Nell, but also to a smaller extent with the Cartographers themselves during the Agloe project. Obsession is clearest in Wally’s character; in fact, it is almost built into him from the beginning. Described as a quiet perfectionist, Wally is always the most resistant to change, but becomes the most adamant support of a new idea, once he has been convinced (usually by Tam). However, Wally’s obsession with Tam leads to his obsession with secrets, and later, control. One Cartographer observes that his feelings for Tam are “like a phantom limb” (144), secret even from himself although he could still feel them.

This is why he doesn’t want to share the secret of Agloe with the others. In his mind, because he and Tam found the map and discovered Agloe, it should remain their secret, but once the other Cartographers are brought in, Wally’s obsession with keeping Agloe secret spirals out of control. Ironically, because Wally is powerless to prevent Tam’s choices, he becomes obsessed with controlling everything else. This mindset is first portrayed through Wally’s robberies and inquiries about other copies of the 1930 General Drafting New York road map on which Agloe is depicted; his collection and subsequent destruction of the maps indicates the extent of his desire for control and implies just how far he might go to maintain it.