Geographic Information Systems
GIS Analysis and Modeling
1. Geographic Analysis
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Geographic questions: where, when, why, and how
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The purpose of the analysis is to answer questions
about:
- what existed at where, when, why, and how
- what will happen at where in the future or in other
locations
2. Organizing Geographic Data
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Data layers (coverage etc.)
Feature types: points, lines, polygons
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Objects: geometric or thematic
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e.g. Development
streets - line layer1
streams - line layer2
parcels - polygon layer1
soils - polygon layer2
3. Maintenance of the Spatial Data
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Format transformation
- Spatial data files must be transformed into the data
structures and file formats used internally by a GIS
software package
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Geometric transformation
- Different data layers are registered to a common
coordinate system
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Conflation
3.(3) Conflation
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The procedure of reconciling the positions of
corresponding features in different data layers (e.g.
snapping).
4. Maintenance of Attribute Data
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Attribute editing
- List, add, delete, redefine, etc.
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Attribute query
- Retrieve attributes according to certain criteria
5. Integrated Analysis of Spatial and
Attribute Data
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The power of GIS lies in its ability to analyze spatial and
attribute data together
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Retrieval, classification, and measurements
Overlay
5. (1) Retrieval, Classification, and
Measurements
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Retrieval
Classification
Measurements
5. (1) (i) Retrieval
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Selective search without modifying the original data (for
output)
http://www.sdsmt.edu/online-courses/geology/mprice/geo416/lecture9.ppt
5. (1) (ii) Classification
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Attribute data
- cerate a new attribute item based on existing ones
Spatial data
-spatial features may be aggregated to larger entities
e.g. Recode in a raster environment
Dissolve in a vector environment
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Single layer vs. multiple layers (overlay)
Classification
Raw data
Classified data
http://www.geog.leeds.ac.uk/courses/level2/geog2750/geog2750_15.ppt
5. (1) (iii) Measurement
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Distances between points
Nearest distances
Functional distances
Lengths of lines
Perimeters and areas of polygons
Centroid of an area
Area of a profile
Volume
Shape
Narrowest and broadest distances across a polygon
Sinuosity of a line
5. (1) (iii) Measurement
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Distances between Points
- Euclidian distance
5. (1) (iii) Measurement
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Nearest distances
The Closest Facility
5. (1) (iii) Measurement
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Functional Distance
Three-minute response time from a fire station, City of Phoenix
http://www.esri.com/mapmuseum/mapbook_gallery/volume17/public2.html
5. (1) (iii) Measurement
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Lengths of lines
Perimeters and areas of polygons
5. (1) (iii) Measurement
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Centroid of an area
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Used to represent a polygons by a single point
Several evaluation methods: mean value,
center of the enclosing circle or
rectangle,
http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf
5. (1) (iii) Measurement
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Area of a profile
Volume
5. (1) (iii) Measurement
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Shape
- how to measure shape of an area?
- a compact shape has a small perimeter for a given area
- compare perimeter to the perimeter of a circle of the
same area - - shape = perimeter / area
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Narrowest and broadest distances across a polygon
5. (1) (iii) Measurement
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Sinuosity of a line
- the ratio of reach length to the straight line distance from
point A (bottom of reach) to point (top of reach)
5. (2) Overlay
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Arithmetic overlay
Logic overlay
Weighting input layers
Raster vs. vector overlay
5. (2)(i) Arithmetic Overlay
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adding layers, subtracting, multiplication, division, etc.
Raster
Input data layer A
Input data layer B
Output data layer
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(2)(i) Arithmetic
Overlay
Arithmetic5.operation
on two data layers
using the vector
data model
Attribute data
Spatial data
Input
data layer A
Input
data layer B
Output
data layer
5. (2)(ii) Logic Overlay
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Finding areas where certain conditions occur
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Boolean logic
Mary Ruvane, UNC –Chapel Hill
5. (2)(iii) Weighting Input Layers
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Professional experiences
Expert votes
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Empirical or analytical models
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5. (2)(iv) Raster vs. Vector Overlay
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Raster
- Every cell is executed, and the overlay result is a new layer
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Vector
- The operation is executed only for areas of interest
- New attribute items are created
- New layers may be created that carry both the original and
new attributes
- The operation is generally more complex than raster overlay
Raster Overlay
Vector Overlay
http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf
Readings
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Chapter 5,6,9,10