The Arkham city section of the board shows the city of Arkham divided into 9 neighborhoods, each of which has between 2 and 3 important locations, as well as a street area. The investigators move around on this section of the board, passing through the streets to visit the various locations. Each location is marked with a number of encounter icons showing some of the most common types of results from encounters at that location.
Cards whose text includes the phrase "in Arkham" apply not only to the Arkham Horror base game, but also to any location or street area on any of the various expansion boards. For example, an Environment card that adds +1 to Fight checks and subtracts –1 from Will checks in Arkham also affects investigators who are, for instance, in a Dunwich (or Kingsport, or Innsmouth) street area or location.
Arkham is first mentioned in The Picture in the House (1920), written by H.P. Lovecraft. It is based on Salem, Massachusetts (of witch trial notoriety).