GIS and Spatial Analysis

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GIS and Spatial Analysis

• Michael F. Goodchild
• University of California
• Santa Barbara

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Outline

• GIS-oriented definitions of spatial analysis
• The role of the GIS
• Taxonomies of spatial analysis
• A six-way classification
• Issues and concerns

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Definitions

• Spatial data
• information about phenomena organized in a
  spatial frame
• the geographic frame
• Methods applied to spatial data that
• add value
• reveal patterns and anomalies
• support decisions

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Spatial analysis

• Methods whose results depend on the locations of
  phenomena in the frame
• are not invariant under relocation
• Some types of relocation may not affect social
  processes
• rotation
• relocation
• inversion

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The geographic frame

• The atomic form ltx,zgt
• Location abstracted
• distance matrix
• adjacency matrix
• invariance under rotation, inversion, relocation

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Spatial analysis as a collaboration

• The computer as butler to the human mind
• Are maps mere?
• Humans as sources of context
• cross-sectional data are already rich in context

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The role of the GIS

• The infrastructure for handling data types
• to spatial data as Excel is to tables, as S-Plus
  is to statistical data, as Word is to text
• spatial data or geographic data?
• the housekeeper
• the editor
• The visualization tool

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The GIS data types

• Discrete geographic features
• points, lines, areas
• the contents of maps
• with associated attributes
• countable
• conceived as tables with associated feature
  geometry
• ESRI shapefiles

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Fields

• Geography as a collection of continuous variables
• measured on nominal, ordinal, interval, ratio
  scales
• vector fields of direction and magnitude
• exactly one value per point
• zf(x)
• population density, land ownership, zoning

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Field representations

• Raster of rectangular cells
• Raster of uniformly spaced points
• Irregularly spaced points
• Irregular areas (polygons)
• Digitized contours
• Triangular mesh (triangulated irregular network
  or TIN)
• ESRI coverages

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GIS as a data access mechanism

• The geolibrary
• place-based search
• integrating information about a place
• making access transparent

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Taxonomies of spatial analysis

• Thousands of methods
• every one a command, menu item, icon,
• Based on data type
• point pattern analysis
• area (polygon) analysis
• analysis of interactions
• Bailey and Gatrell, Haining, Unwin

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A six-way conceptual classification

• Query and reasoning
• Measurement
• Transformation
• Descriptive summary
• Optimization
• Hypothesis testing

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Queries and reasoning

• Real-time answers to geographic questions
• Where is?
• What is this?
• How do I get from here to here?
• Based on alternative views of a database

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Measurements

• Area
• Distance
• Length
• Perimeter
• Slope, aspect
• Shape

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Transformations

• Buffering
• Points in polygons
• Polygon overlay
• Spatial interpolation
• Density estimation

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Courtesy of Dick Block
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Descriptive summary

• Centers
• Measures of spatial dispersion
• Spatial dependence
• Fragmentation
• Fractional dimension

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Optimization

• Design to achieve specific objectives
• Location of central point-like facilities to
  serve dispersed demand
• Location of linear facilities
• Design of boundaries for elections

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Hypothesis testing

• Geographic objects as a sample from a population
• what is the population?
• The independence assumption
• the First Law of Geography
• failure to find spatial dependence is always a
  Type II error
• hell is a place with no spatial dependence

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Issues and concerns

• Limits to representation
• Geographic or spatial?
• site or situation?
• The critical perspective

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1990
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Information lost to the representation

• All sub-polygon spatial variation
• All within-decade temporal variation
• All identities
• instead of ltxy, persongt we have
• ltR, numbergt
• ltxy, xy, xy, xy, , Rgt

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Challenges of GIS

• How to characterize what is missing?
• error, accuracy, uncertainty
• How to choose the best representation?
• confounding influences
• How to support many data models in a single
  software package

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Weaknesses of GIS

• There are too many possible data models
• special-purpose GIS
• lack of interoperability
• Difficult to add data models retroactively

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Brian Harley

• Maps as reflections of the agendas of their
  makers
• deconstructing the map
• Maps as essential tools of imperial power
• Whose agenda is in your glove compartment?
• Dennis Wood, The Power of Maps

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The Gulf War the first GIS war

• Digital maps
• GPS in tanks, aircraft, hand-held by infantry
• Precise routing and targeting of cruise missiles
  and smart bombs
• Satellite surveillance

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Another dimension to the critique

• GIS presents one view
• privileged
• rational, scientific, positivist
• vertical, God-like, masculinist
• precise boundaries, sharp edges
• John Pickles, Ground Truth The social
  implications of GIS (1995)

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It's very pleasant today in Santa Barbara
Spoken word
Text
Picture
x, y, T
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The GIS-2 agenda

• A reinvented technology
• more humanistic in approach
• reflecting multiple views of the world
• human complexity and vagueness

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Naïve Geography

• What people believe about the world
• The continental US as a rectangle
• Seattle is due N of San Diego
• New York is due N of Miami
• Options for GIS designers
• something a child of 10 can use
• something for an expert Spatially Aware
  Professional