GIS and Spatial AnalysisGIS and Spatial Analysis

Michael F. Goodchild

University of California

Santa Barbara

OutlineOutline

GIS-oriented definitions of spatial analysis

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

DefinitionsDefinitions

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

Spatial analysisSpatial 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

The geographic frameThe geographic frame

The atomic form <x,z> Location abstracted

– distance matrix– adjacency matrix– invariance under rotation, inversion,

relocation

Spatial analysis as a collaborationSpatial 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

The role of the GISThe 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

The GIS data typesThe 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

FieldsFields

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– z=f(x)– population density, land ownership, zoning

Field representationsField 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

GIS as a data access mechanismGIS as a data access mechanism

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

Taxonomies of spatial analysisTaxonomies 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

A six-way conceptual classificationA six-way conceptual classification

Query and reasoning Measurement Transformation Descriptive summary Optimization Hypothesis testing

Queries and reasoningQueries 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

MeasurementsMeasurements

Area Distance Length Perimeter Slope, aspect Shape

TransformationsTransformations

Buffering Points in polygons Polygon overlay Spatial interpolation Density estimation

City limits

Areas reachable in 5 minutes

Areas reachable in 10 minutes

Other areas

Courtesy of Dick Block

Descriptive summaryDescriptive summary

Centers Measures of spatial dispersion Spatial dependence Fragmentation Fractional dimension

OptimizationOptimization

Design to achieve specific objectives Location of central point-like facilities to

serve dispersed demand Location of linear facilities Design of boundaries for elections

Hypothesis testingHypothesis 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

Issues and concernsIssues and concerns

Limits to representation Geographic or spatial?

– site or situation? The critical perspective

1990

1564

2886

995

Information lost to the representationInformation lost to the representation

All sub-polygon spatial variation All within-decade temporal variation All identities

– instead of <xy, person> we have

<R, number>

<xy, xy, xy, xy, …, R>

Challenges of GISChallenges 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

Weaknesses of GISWeaknesses of GIS

There are too many possible data models– special-purpose GIS– lack of interoperability

Difficult to add data models retroactively

Brian HarleyBrian 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

The Gulf War: the first GIS warThe 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

Another dimension to the critiqueAnother 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)

Spoken word

Text

Picture

x, y, T

It's very pleasant

today in Santa Barbara

The GIS-2 agendaThe GIS-2 agenda

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

Naïve GeographyNaïve 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