Any two or more cells with the same value belong to the same zone. A zone can consist of cells that are adjacent, disconnected, or both. Zones whose cells are adjacent usually represent a single feature of an area, such as a building, road, or water body. Assemblages of entities, such as forest stands in a state, soil types in a county, or single-family houses in a town, are features of an area that will most likely be represented by zones made up of many disconnected groups of connected cells (regions).
Every cell in a raster belongs to a zone. Some raster datasets contain only a few zones, while others contain many.
Each group of connected cells in a zone is considered a region. A zone that consists of a single group of connected cells has only one region. Zones can be composed of as many regions as necessary to represent a feature—the number of cells that make up a region has no practical limits. The ArcGIS Spatial Analyst extension provides the tools needed to turn regions into individual zones. In the previous raster dataset example, Zone 2 consists of two regions, Zone 4 of three regions, and Zone 5 of one region.