In the not-so-distant future world of Infinite Jest, the USA, Canada and Mexico have merged to form one unified state - the Organisation of North American Nations (O.N.A.N.). Perhaps not coincidentally, Onan was a biblical character associated with masturbation (Genesis 38:9).
The Great Concavity/Convexity lies just south of the Canadian border. Further south is Boston, Massachusetts on the north-east coast, location of the Enfield Tennis Academy and Ennet House Drug and Alcohol Recovery House. Slightly to the west is Syracuse, New York, where David Foster Wallace lived when he wrote Infinite Jest in 1996. In the west is the state of Arizona, where Orin Incandenza makes his living as a punter for the Arizona Cardinals football team. In the same state is Tucson, home of the U.S. Office of Unspecified Services, and this is also where Remy Marathe and Hugh Steeply meet.
The novel's primary locations are the Enfield Tennis Academy and Ennet House Drug and Alcohol Recovery House. The two buildings are separated by a hillside in suburban Boston, Massachusetts. Many of the novel's characters are students or faculty at the school or patients and staff at the halfway house.
Much of what used to be the northeastern United States and southeastern Canada has become a hazardous waste dump known as the "Great Concavity" to the Americans and as the "Great Convexity" to Canadians. Located north of the horizontal line between Buffalo and Northeastern Massachusetts the Concavity/Convexity was carved into the landscape and given to Canada ostensibly as a gift.
In truth, it's O.N.A.N. President Johnny Gentle's way of reducing the pollution problem that pervades the former United States - the Concavity/Convexity is actually toxic wasteland, with giant catapults situated near Boston hurling waste northward into the void.
The map above has been modified to include the borderline of the Great Concavity/Convexity, based on the descriptions of the locations given below.
It has a concavity. It looks sort of like some person or persons have taken a deep wicked canine-intensive bite out of its upper right bit, in which an ascending and then descending line has its near-right-angle at what looks to be the historic and now hideously befouled Ticonderoga NY. (403)
Massive lucite walls south of what used to be Syracuse, Concord NH, Salem, MA. (438)
Move south, calmly and in all haste, toward some border metropolis - Rome NNY or Glen Falls NNY or Beverley MA. (93)
Quebec is a province in east-central Canada, with a predominantly French-speaking identity. The left-wing political group Parti Quebecois advocates independent sovereignty and secession from Canada. The issue of separatism is a prevailing theme in Infinite Jest.
Les Assassins des Fauteuils Roulants (Wheelchair Assassins) are an extremist Québécois separatist group that developed after Canada and Mexico joined the United States in forming the Organisation of North American Nations.
Orin Incandenza is a punter for the Arizona Cardinals. The novel begins, chronologically, at the end, with Orin's younger brother Hal interviewing for a position at the University of Arizona.
Outside of Tucson is the U.S. Office of Unspecified Services; one of their operatives, Hugh Steeply, meets Remy Marathe in the desert for a conversation which is spread across several chapters.