Geographic Information Systems

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Geographic Information Systems

• GIS Analysis and Modeling

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1. Geographic Analysis

• Geographic questions where, when, why, and how
• 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

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2. Organizing Geographic Data

• Data layers (shape file etc.)
• Feature types points, lines, polygons
• Object types geometric or thematic
• e.g. Development
• streets - line layer1
• water - line layer2
• parcels - polygon layer1
• soils - polygon layer2

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3. Maintenance of the Spatial Data

• Format transformation
• - Spatial data files must be transformed into
  the data structures and file formats used
  internally by a GIS software package
• Geometric transformation
• - Different data layers should be registered to
  a common coordinate system

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4. Maintenance of Attribute Data

• Attribute editing
• - List, add, delete, redefine, etc.
• Attribute query
• - Retrieve attributes according to certain
  criteria

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5. Integrated Analysis of Spatial and Attribute
Data

• The power of GIS lies in its ability to analyze
  spatial and attribute data together
• Retrieval, classification, and measurements
• Overlay

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5. (1) (i) Retrieval

• Selective search without modifying the original
  data (for output)

http//www.sdsmt.edu/online-courses/geology/mprice
/geo416/lecture9.ppt
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5. (1) (ii) Classification

• 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
• Single layer vs. multiple layers (overlay)

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Classification
Raw data
Classified data
http//www.geog.leeds.ac.uk/courses/level2/geog275
0/geog2750_15.ppt
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5. (1) (iii) Measurement

• 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

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5. (1) (iii) Measurement

• Distances between Points
• - Euclidian distance

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5. (1) (iii) Measurement

• Nearest distances

The Closest Facility
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5. (1) (iii) Measurement

• Functional Distance

Three-minute response time from a fire station,
City of Phoenix
http//www.esri.com/mapmuseum/mapbook_gallery/volu
me17/public2.html
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5. (1) (iii) Measurement

• Lengths of lines
• Perimeters and areas of polygons

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5. (1) (iii) Measurement

• Centroid of an area
• It is used to represent a polygon by a single
  point
• Several methods to identify a centroid mean
  value of vertices coordinates, center of the
  enclosing circle or rectangle,

http//www.geoict.net/tgipage/Teaching/UNIT207--P
PT.pdf
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5. (1) (iii) Measurement

• Area of a profile
• Volume

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5. (1) (iii) Measurement

• 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
• Narrowest and broadest distances across a polygon

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5. (1) (iii) Measurement

• Sinuosity of a line - the ratio of the actual
  length to the straight line length between point
  A and point B

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5. (2) Overlay

• Arithmetic overlay
• Logic overlay
• Weighting input layers
• Raster vs. vector overlay

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5. (2)(i) Arithmetic Overlay

• adding layers, subtracting, multiplication,
  division, etc.
• Raster

Input data layer A
Input data layer B
Output data layer
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5. (2)(i) Arithmetic Overlay

• Arithmetic 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
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5. (2)(ii) Logic Overlay

• Finding areas where certain conditions occur
• Boolean logic

Mary Ruvane, UNC Chapel Hill
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5. (2)(iii) Weighting Input Layers

• Professional experiences
• Expert votes
• Empirical or analytical models

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5. (2)(iv) Raster vs. Vector Overlay

• Raster
• - Every cell is executed, and the overlay result
  is a new layer

• 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

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Raster Overlay
Vector Overlay
http//www.geoict.net/tgipage/Teaching/UNIT207--P
PT.pdf
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Readings

• Chapter 5,6,9,10

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3.(3) Conflation

• The procedure of reconciling the positions of
  corresponding features in different data layers
  (e.g. snapping).