Reading Assignment: Bolstad Chapters 10 & 11 Spatial Analysis (Raster)
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Transcript of Reading Assignment: Bolstad Chapters 10 & 11 Spatial Analysis (Raster)
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Reading Assignment: Bolstad Chapters 10 & 11
Spatial Analysis (Raster)
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• Spring Break Next Week!• During break fill out address form for ~ 20 places
– Will be used later in lab for Home Range analysis
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Raster Data Model
Uses grid cells of a given dimension to represent the value or attribute of a real world entity or phenomenon.
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• In a raster layer, the cells are arranged in rows and columns.
• All cells in a raster layer are the same size.
• Cell Size = Spatial Resolution: the dimension of the area covered on the ground and represented by a single cell (e.g., 10m).
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• The value may be a measurement or a code.
• Cell values are numeric: can be either positive or negative, integer, or floating point.
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Applications– Predictive modeling– The fate of pollutants– Fire spread– Determine erosion potential – Estimates of forest growth– Change detection
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Map Algebra: • Dana Tomlin and Joseph Berry (1970’s)• A method of treating individual raster layers as
members of algebraic expressions.
2 * LayerA
Raster is Faster!Vector is corrector
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Arithmetic Operators (+, -, *, /)
Mathematical Functions (Sqr, Sqrt, Log, Abs, exp, int, etc.)Comparison Operators (>, >=, =, <>, <, <=)Boolean Operators (AND, OR, NOT, XOR)
Map Algebra: LayerA + LayerB
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Map Algebra:
Input
Output
LayerA * LayerB
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Raster Calculator(for map algebra)
Spatial Analyst (extension for working
with raster data)
Converting feet to meters
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Probability of encountering the cascade treefrog (Litoria pearsoniana) within the forests of eastern Australia:
1 / (1 + exp(10.48 – 2.204 * log10(RAINFALL) – 2.037 * PALMS))
RAINFALL= the annual volume of rain falling in the watershed above the stream PALMS = 1 if palms are present at the site and 0 otherwise.
Map Algebra Examples:
Fire Hazard:[Fuel Density Hazard] + [Slope Hazard] + [Veg Type Hazard]
Probability of success for entrepreneurs in Mendocino County
1 / (1 + exp(-(1.010e + 0) + (6.409e-02 * acreage) + (-7.100e-06 * land_value) + (-2.797e-01 * CE_count) + (-1.234e-02 * tot_pop))))))
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Green = suitable aspect (cell value = 1)Red = unsuitable aspect (cell value = 0)
Slope < 20 degrees South facing slopes aspect between 150 and 200 degrees.
Identifying suitable habitat
Green = suitable slope (cell value = 1)Red = unsuitable slope (cell value = 0)
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“suitable aspect” * “suitable slope”
suitable_habitat
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Cell value = 1…Suitable slope & Suitable aspect
1 0 0 1
1 1 0 0
0 0 0 1
0 1 0 1
0 0 0 0
0 1 1 0
1 1 0 1
1 1 0 1
0 0 0 0
0 1 0 0
0 0 0 1
0 1 0 1
* =
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Slope < 20 degrees South facing slopes aspect between 150 and 200 degrees.
?
Reclassification
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Reclassification:
Assigns new output values that depend on the specific sets of input values (usually defined by a range of values)
1
1 1
1
1 1
1
1 2
2
1
2 3
44
4
2
3
4
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0
Identify Slope < 20 degrees
Reclassify
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Comparison operators
<
Layer 1 Layer 2
=
Comparing the cell value in one layer to the cell value in another layer.N = No Data
(>, >=, =, <>, <, <=)
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Identify Slope < 20 degrees
(Alternative method)
“Slope” < 20
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Boolean operatorsLayer 1 Layer 2
Output = 1 whereboth input cells aresomething other than0 or “N” (No Data)
Output = 1 whereone input cell or the other is something other than 0 or “N”
Output = 1 where input cell is a 0
(AND, OR, NOT, XOR)
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XOR
[RAINFALL] > 20 XOR [SLOPE] < 35
Boolean operators
If the rainfall value is 21 and the slope value is 34 at a particular location, what would the output cell value be at that location?
0
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Finding cells within a specific elevation range (500 -1000m)
Combining Boolean & Comparison Operators (1 raster layer)
1
0
"dem" > 500 and "dem" < 1000
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Finding elevations between 20 and 500m where slope is less than 30 degrees
Combining Boolean & Comparison Operators (2 raster layers)
"DEM" > 20 and "DEM" < 500 and "slope" < 30
1
0
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• Elevation• Slope• Aspect• Viewshed• Hillshade
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Deriving terrain variables (e.g., slope, aspect) from a DEM
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The direction (in compass angles) that a cell’s slope faces.
Determines …
1) Which way water will flow
2) amount of sunlight a site may receive
3) which portion of a landscape is visible from a
viewing point
N
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The viewshed for a point is the collection of areas visible from that point.
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