Spatial Analysis

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Spatial Analysis vector data analysis

• L2
• 1/28/2008

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Recap three data models

• Vector
• Raster
• Geodatabase (object-oriented data model)
• Vector data and table
• feature class is the basis
• Raster data

The real world is complex. Neither discrete
(object) nor continuous (field) can perfectly
represent some of real world situations. We need
combined model dual, hybrid, or object-oriented
approach
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Spatial Analysis tools in ArcToolBox
Vector data analysis Shapefile Feature
class/table
Raster data analysis
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Details
Vector
Raster
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1. Extract

• To create a new subset from the input (shapefile,
  features and attributes in a feature class or
  table) based on spatial intersection or an
  attribute query.
• Clip
• Select
• Split
• Table select

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Clip
XY tolerance The minimum distance separating
all feature coordinates (nodes and vertices) as
well as the distance a coordinate can move in X
or Y (or both). You can set the value to be
higher for data that has less coordinate accuracy
and lower for datasets with extremely high
accuracy.
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Select
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Split
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Table select
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2. Overlay

• Joining two existing sets of features into a
  single set of features to identify spatial
  relationships between the input features.
• Erase
• Identify
• Intersect
• Spatial Join
• Symmetrical difference
• Union
• Update

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3. Proximity

• Identify features that are closest to one
  another, calculate the distances around them, and
  calculate distances between them.
• Buffer
• Multiple ring buffer
• Create Thiessen Polygon
• Near
• Point distance

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Not dissolved
Dissolved
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Example
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How to form Thiessen polygons

• Also known as 'Voronoi networks' and 'Delaunay
  triangulations', Thiessen polygons were
  independently discovered in several fields of
  study, including climatology and geography. They
  are named after a climatologist who used them to
  perform a transformation from point climate
  stations to watersheds.
• Thiessen polygons can be used to describe the
  area of influence of a point in a set of points.
  If you take a set of points and connect each
  point to its nearest neighbor, you have what's
  called a triangulated irregular network (TIN). If
  you bisect each connecting line segment
  perpendicularly and create closed polygons with
  the perpendicular bisectors, the result will be a
  set of Thiessen polygons. The area contained in
  each polygon is closer to the point on which the
  polygon is based than to any other point in the
  dataset.

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Statistics

• Basic statistic to the attribute table
• Frequency
• Summary statistics

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