This document discusses key concepts in raster GIS including: - Raster representation involves organizing geographic data into a grid of equally-sized cells. - Raster data can be discrete/categorical with data classified into different land cover types or continuous, storing surfaces like elevation as unique values. - Rasters can have multiple bands of data and discrete rasters can include attribute tables. - Resolution refers to the size of grid cells, with higher resolution meaning smaller cells and more detail but larger file sizes. - Mixed pixels can occur along feature edges where a cell value averages multiple land cover types.

1. Raster GIS
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2. RASTER REPRESENTATION
RASTER PROPERTIES
RASTER TESSELLATION
RASTER ANALYSIS
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3. Raster Representation
Raster Properties
Raster Tessellation
RASTER ANALYSIS ASSIGNMENT HELP
Why, what, where?
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4. Raster Representation
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5. Rasters contain observed or derived
data, or both.
Data sources include:
• Sample points monitoring stations,
elevation points): Resulting raster:
air pollution surface, digital
elevation model
• Classification of imagery (e.g.,
satellite image): Resulting raster:
land-cover grid
• Conversion of vector data
Raster Data Sources
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6. A raster is a grid of cells that
are equally spaced according
to the cell size.
The grid extends between the
top left and bottom left
coordinate (the extent) based
on cell size and number of
rows/columns
Raster Representation
Review
Mixed conifer
Douglas fir
Oak savannah
Grassland
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7. • Refers to a limited number of
classes
• Pixels with same value belong
to same class
• Numeric type: integer
• Pixels not belonging to a class
are denoted, 0 or 9999 or
NoData
• Examples: soil type
RASTER DISCRETE
CATEGORICAL
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8. A raster is
typically comprised
of one band, but can
be made up of
multiple bands.
Raster Discrete
Multi Bands
Imagery is a good example of
this, but it is possible to have
a raster with different data
types. GLOBALWEBTUTORS.COM

9. If your raster is a
single band of an integer
type (and only if), a
raster can have an
attribute table.
RASTER DISCRETE ATTRIBUTES
CAN HAVE AN ATTRIBUTE TABLE?
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10. Let’s say we have a
road raster, what
attributes could be
stored?
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11. • A continuous raster stores surfaces
or fields of variables that change
continuously over space (Elevation –
DEM)
• Many potential values
• Adjacent cells rarely share the same
value.
Raster Continuous
A single variable
Air photo
DEM
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12. • Unlimited number of values
within a fixed range
• Each is unique - no classes
(even if same value)
• Numeric Type: decimal
numbers (floating point)
• Also called a surface
Raster Continuous
A SINGLE VARIABLE
2.1 2.3 2.4 2.6 2.9 3.1 3.5
1.9 2.2 2.3 2.5 2.7 3.0 3.4
1.8 2.0 2.1 2.4 2.7 3.0 3.4
1.7 1.9 2.1 2.3 2.7 2.9 3.3
1.7 1.8 2.0 2.3 2.6 2.8 3.1
1.7 1.8 1.9 2.3 2.5 2.5 2.9
1.6 1.7 1.8 1.9 2.1 2.3 2.7
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13. Resolution (pixel size):
Size of the grid cell or picture element,
defining the level of spatial detail in
ground units (e.g., 10 m)
The “fineness” of the grid defines the file
storage space. Data volume equals the
number of pixels X number type
RASTER RESOLUTION
Trade-off between detail and file size
Cell = 7m x 7m = 49m2
Area?
Cell = 10m x 10m = 100m2
Area = 7x7x100m2 =4900m2
700 meters
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14. A pixel whose value represents the average of several
classes within the area that it covers on the ground.
They are common along edges of features, and in
heterogeneous landscapes (e.g. urban areas).
MIXED PIXEL PROBLEM
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