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ENV510 Landscape Ecology and GIS
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| Spatial | Attribute
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| Modelling | Software
Integrated analysis
of spatial and attribute data
These GIS
operations are especially applicable to environmental modelling.
Retrieval/classification/measurement
functions
Spatial
and attribute data are retrieved but only the attribute data are modified or
created, no changes are made to the spatial elements.
- Retrieval
operations involved selective search, manipulation and output of data.
- Classification
is the procedure of identifying a set of features belonging to a group and
assigning a name to that group.
- Measurement
functions is the calculation of distances
between points, length of lines, perimeters and areas of polygons and the
size of a group of cells with the same class.
Overlay
operations
This is divided into arithmetical
and logical overlay.
- Arithmetical
overlay includes addition, subtraction, division and multiplication
of each value in the data layer by a value in the corresponding location in
another data layer
- Logical
overlay involves finding locations where a specified set of conditions
occur or do not occur together
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Neighbourhood
operations
These evaluate
the characteristics of the area surrounding a specified location - include operations
such as search, line in polygon, point in polygon, topographic functions, theissen
polygons, interpolation, contour generation
- Search
assigns a value to each target feature according to some characteristic of
its neighbourhood. The search area is commonly a square, rectangle or circular
with the size selected by the operator. The search area is often termed a
'window'. There are 2 types of search functions - those that operate on numerical
data and those that operate on thematic data
- Numeric
functions
are functions like the total, average, maximum, minimum and measures of
diversity (variance or standard deviation)
- Thematic
functions are functions like the majority,
maximum, minimum and diversity (number of different classes)
- Line-in-polygon
and point-in-polygon operations this
is the identification of points and lines contained within polygons. In vector
GIS this is a search function in raster GIS this is essentially an overlay
operation.
- Topographic
functions topography relates to surface
characteristics ie relief. Topographic functions are used to calculate values
that describe the topography at specific geographic locations or in the vicinity
of locations eg aspect at the location or slope of the area around the location.
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- Thiessen
polygons define the areas of influence around each point in a set
of points. Thiessen polygons are constructed round points so that the polygon
boundaries are equidistant from the neighbouring points.
- Interpolation
is the procedure of predicting unknown values using known values at neighbouring
locations.
- Contour
generation Contouring
is the procedure of connecting data points with the same value to construct
lines that portray the relief of the surface. GIS make use of interpolation
techniques to generate missing data points
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Connectivity
functions
These are
operations that use functions that accumulate values over the area being traversed
eg contiguity measures, proximity, network, spread, seek, intervisibility, illumination,
perspective view.
- Contiguity
measures evaluate characteristics of spatial units that are connected.
Common measures are the size of the contiguous area and shortest and longest
straight-line distances across the area.
- Proximity
is a measure of the distance between features. A common proximity function
is buffer zone generation. A buffer zone is an area of specified width drawn
around one or more map features.
- Network
functions A network is a set of interconnected
linear features that form a pattern or framework. Networks are commonly used
for moving resources from one location to another. There are 3 principal types
of network analyses that GIS perform
- network
loading eg predicting flows of water
through a stream network
- route
optimisation eg routing of emergency
vehicles
- resource
allocation
eg division of an area into service zones
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- Spread
evaluates phenomena that accumulate with distance eg it can be used to evaluate
transportation time or cost over a complex surface. Spread functions have
characteristics of proximity and network functions. They can generate accumulation
surfaces.
- Seek
(or stream function) performs a directed search
outward in a step-by-step manner from a start location using a specified decision
rule.
- Intervisibility
(viewshed modelling) can be used to map the area visible from certain locations
eg from a scenic lookout. A viewshed is an area that can be seen from specified
target locations. These functions make use of digital elevation data.
Viewshed
- Illumination
portrays the effect of shining a light onto a 3-dimensional surface. The output
is a shaded relief image. This function is controlled by:
- the
position of the illumination source,
- the
topography and reflectance of the surface
- the
position and direction from which the model is viewed
- Perspective
A perspective view is a surface portrayed from a viewing position other than
vertical. These are primarily presentation tools, useful for showing 3-dimensionality
of features on a surface.
(Aranoff,
1989)
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