Site Selection

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Site Selection Making Spatial Decisions Using
GIS
IAP 2006 1/30/06
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Why would I use Site Selection Tools?

• Decide on an appropriate location for a new
  building
• Uncover areas of risk for geologic hazards
• Pinpoint areas for development
• Establish safe zones for habitation

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Add Layers of Data to GIS

• Census
• Infrastructure
• Environmental

Analyze Layers Together
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Data issues in vector processing

• The world is complex and data represents a
  simplified version
• In vector data, objects are represented as
  points, lines and polygons
• To get data into a GIS, two procedures are used,
  selection and representation

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Selection of features for use in a GIS

• Only details of interest to the creator are
  stored in the data.
• Metadata who made the data and why you should
  use it, or not!

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Representation of data

• Tied to scale and data type
• City as point or polygon? Do you need to see the
  area of a city?
• Road centerlines vs. entire road system (usually
  to the curb)
• Vector objects in a GIS have defined boundaries,
  unlike nature (transition in forests)

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Overlay operations in a GIS

• Origins in Landscape Planning
• Set theory polygons represent sets, overlay
  represents intersects, unions and symmetrical
  difference
• Computational Geometry

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Some Analysis Tools

• Spatial join
• Clip
• Intersect
• Union
• Symmetrical Difference
• Buffer

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Spatial Join
Point in polygon operation which points are in
the Polygon?
Polygon ID (id_1) is added to the point layers
attribute table.
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Clip
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Intersect
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Union
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Symmetrical Difference
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Buffer
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Things to consider

• Vector data processing is CPU intensive.
• There are no error data produced as a result of
  overlay operations.
• inaccurate data in inaccurate data out
• (may be more inaccurate after processing)