The Arkham city board is divided into areas called neighborhoods, each of which contains several locations connected to a street area. The different neighborhoods of the board are in turn connected by movement lines between their street areas. Neighborhoods are usually based on a theme, with the locations and the available encounters in those locations revolving around that theme.
Each of the major expansions adds a board for a new town such as Dunwich, Kingsport, or Innsmouth. These boards add a new set of neighborhoods and a new set of Arkham Location Cards associated with for each neighborhood.
Arkham Location Cards
Each neigborhood on the original Arkham city board or the expansion boards has a small deck of cards associated with it. These represent encounters which the investigators may have in that location, and are often referred to as the Encounter deck.
During the Arkham Encounters Phase of the turn, investigators who are in a location other than the street and have an encounter in this neighborhood may have that encounter by drawing from this neighborhood's deck, and reading and following the instructions for this specific location from that card.