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

Figure 4.4: Surface map raster [16].
Figure 4.5: Thematic map raster [16].
photographs, scanned documents or scanned drawings are conserved. Via raster representation,
these real phenomena can also be used as user-defined attributes of a geographic object. For
example, a parcel layer may have scanned legal documents identifying the latest transaction for
that parcel. Or, a layer representing cave openings may have pictures of the actual cave openings
associated with the point features. Concretely, a real tree represented by the digital picture in
Figure 4.6 can be used as an attribute to a landscape layer that a city may maintain.
4.4.2 Cell Representation
Figure 4.6: Tree attribute [16].
Raster data is made up of a matrix of cells (or pixels), where each cell contains a value. In other
words, the cell values are used to represent phenomenon described by the raster data such as a category,
magnitude, height or spectral value. The category can be a land-use class such as grassland, forest
or road. A magnitude might represent gravity, noise pollution or percent rainfall. Height (distance)
can represent surface elevation above mean sea level, which can be used to derive slope, aspect and
watershed properties. Spectral values are used in satellite imagery and aerial photography to represent
light reflectance and color.
Cell values can be either positive or negative, integer or floating point. Integer values are best used
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