PostGIS Raster : Extending PostgreSQL for The Support of ... - CoDE

the matrix are parallel to the x-axis and the columns to the y-axis of the Cartesian plane. Row and
column values begin with 0.
Figure 4.11: Pixel or cell location.
The extent of a raster then is defined by the top, bottom, left and right coordinates of the rectangular
covered by the raster, as shown in Figure 4.12 .
4.4.3 Zones and Regions
Zones
Figure 4.12: Raster extent [16].
Any two or more cells with the same value belong to the same zone. A zone consists of cells that are
adjacent, disconnected or both. Zones whose cells are adjacent usually represent a single feature such
as a building, lake, 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 that will most likely be represented
by zones made up of many disconnected groups of connected cells.
Every cell in a raster belongs to a zone. Some raster data contains only a few zones while others
contain many.
Regions
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. In the example of Figure 4.13, zone 2 consists of two regions, zone 4 of three
regions and zone 5 of one region.
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