Nearest and Containment Vector Spatial Analyses, Spatial Data Management

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UST/ENV/PAD/PDD 642/742 Introduction to
Geographic Information Systems
Lecture 6-2 Vector GIS Concepts and Operations
II Geoprocessing
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Introduction to Geoprocessing

• One of the most powerful components of a GIS
• Processing of geographic information to create
  new information by applying an operation to
  existing data
• Based on a framework of data transformation
  (spatial data manipulation)
• More than 200 geoprocessing tools in ArcGIS
  (common tools Append, Buffer, Clip,
  Dissolve(Aggregation), Intersect, Merge, Union)

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Dissolve Operation (Geoprocessing of ArcGIS 9.1)
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Merge Operation (Geoprocessing of ArcGIS 9.1)
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Buffer Operation (Geoprocessing of ArcGIS 9.1)
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Buffering Features

• The Buffering process creates polygon features
  whose perimeters are at a constant distance
  from input features
• Several concentric buffers can be produced
  in a single operation
• Overlapping buffers may be merged, in order to
  avoid double-counting errors when doing
  point-in-polygon analyses
• Polygon buffers may be drawn at specified
  distances either inside or outside the polygon
  input feature
• The outpur polygon theme has the same
  coordinate system as that of the DataFrame, if
  you are using ArcMap

Multiple Ring Line Buffers
Multiple Ring Point Buffers with dissolved
overlaps
Multiple Ring Polygon Buffers Inside and Outside
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Clip Operation (Geoprocessing of ArcGIS 9.1)
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Clipping Process

• Clipping is an operation used to trim the
  extents of features in existing data sets
  using the features of other data sets
• The input layer features are clipped by
  using the overlay layer features as a sort of
  cookie cutter
• Note that all the original attributes of the
  input layer features are retained, even though
  the shape and area of the output features are
  different, and the coordinate system of the
  DataFrame is used
• Clipping may be used for aesthetic purposes to
  good effect

Overlay theme
Input theme
Before the Clip Operation
After the Clip Operation
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Polygon Overlays (Intersections and Unions)

• Many vector operations include analyses of two
  themes simultaneously
• Typically, these operations are termed
  overlays and can include intersect and
  union operations
• Intersect operations are valid between line and
  polygons themes or between polygon and polygon
  themes
• Union operations are valid between polygon and
  polygon themes only
• In general, overlay processes are used because
  vector boundaries of two data sets rarely
  coincide
• Overlay processes in most cases, require an
  area -weighting scheme for transferring numeric
  attributes from the input themes to the result
  theme

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Intersect Operation (Geoprocessing of ArcGIS 9.1)
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Intersect Process

• The Intersect process computes the geometric
  intersection of all features in the two themes
  and places the results in a new theme
• The input theme can be a line or polygon theme.
  
• The overlay theme must be a polygon theme.
• The overlay theme's features will split the
  input theme.
• Any features in the input theme that are not
  overlaid by features in the overlay theme will
  not be added to the new theme -- that is, if an
  input feature does not intersect any of the
  overlay features, it will not appear in the
  result theme
• The output themes features will be of the same
  type as the input theme features
• During the intersect process, an attribute
  table for the result theme will be created and
  the attribute table for the result theme will
  include the attributes from both the input and
  overlay themes

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Base Data for Intersecting Polygon with Polygon
Base Data for Polygon Intersecting Polygon Overlay
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Intersecting Polygon by Polygon
Results of the Polygon-Polygon Intersect Process
with area-weighted transfer of polygon attributes
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Intersecting Polygon by Polygon Tables
intersect
Trees ( AREA / B_AREA ) Trees
Pop ( AREA / A_AREA ) Pop
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Union Operation (Geoprocessing of ArcGIS 9.1)
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Union Process

• The Union process between an input theme and an
  overlay theme produces a result theme
  containing ALL the features AND attributes
  of two polygon themes
• The result (union) theme contains the total
  spatial combination of information with
  attribute data from both the input and overlay
  polygon themes
• The result theme extents will be the combined
  extents of the input and overlay themes, and
  the result theme will contain attributes from
  both the input and overlay themes

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Base Data for Polygon Union Polygon Overlay
Base Data for Polygon Union Polygon Overlay
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Input-Overlay Results of the Union Process
Results of the Polygon-Polygon Union Set B as
Input and Set A as Overlay
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Input-Overlay Tables showing Results and
Recalculations
union