How people visually explore geospatial data Urška Demšar Geoinformatics, Dept of Urban Planning...
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Transcript of How people visually explore geospatial data Urška Demšar Geoinformatics, Dept of Urban Planning...
How people visually exploreHow people visually exploregeospatial datageospatial data
Urška DemšarGeoinformatics, Dept of Urban Planning and EnvironmentRoyal Institute of Technology (KTH), Stockholm, Sweden
ICA WS on Geospatial Analysis and Modeling8th July 2006
Vienna
Developing geovisualisation tools
Developing a usable and useful information system
User-centred design
Human-Computer Interaction (HCI)
Knowledge about users and how they use the system
Geovisualisation toolsand systems
visual exploration
analysis
presentation
of geospatial data
For a long time: technology-driven development
A recent shift in attitude: user-centred development
Usefulness
Utility
Usability
Can the functionality of the system do what is needed?
How well can typical users use the system?
Usability evaluationProcess of systematically collecting & analysing data on how users use the system for a particular task in a particular environment.
User-centred design
Usability of an information system is the extent to which the system supportsusers to achieve specific goals in a given context of use and to do soeffectively, efficiently and in a satisfactory way. Nielsen 1993
of a computersystem
Evaluate system’s functionality
Assess users’ experienceIdentify specific problems
Usability testing
Formal evaluation
Exploratory usability
User testing
Observing users
Measuring the accuracy and efficiency of users’performance on typical tasks
Assessing how theusers work with thesystem
performingpredefined
tasks
questionnaires
thinking-aloudmethodology
observation,video
controlled measurements:errors, time
descriptive data: verbal protocols
Qualitativeevaluation
Quantitativeevaluation
Methods complement each other!
evaluation throughuser participation
Exploratory usability experiment
GeoVISTA - basedvisual data mining system
Dataset with clearly observable spatial and other patterns
Exploratory usabilityexperiment
How peoplevisually explore geospatial data?
Which explorationstrategies theyadopt?
Which visualisationsthey prefer to use?
Formal usabilityissues: Edsall 2003,Robinson et al. 2005
Data
Iris setosa Iris versicolor Iris virginica
Iris dataset - famous frompattern recognition
Fischer 1936
150 plants, 50 in each class, 4 attributes
Linear separability in attribute space
Original dataset
new attributesplant measurements
bedrocksoil
landuse
put in a spatialcontext
Linear separability in geographic space
Visual data mining:Data mining method which uses visualisation as a communication channel between the user and the computer to discover new patterns.
Data exploration by visual data mining
Data mining = a form of pattern recognition
the human brain
The best patternrecognition apparatus
How to use it in data mining?
Computers communicate with humans visually.
Computerised data visualisation
Visualisations
geoMap
Multiform bivariate matrix
Parallel Coordinates Plot (PCP)
Brushing &linking +
interactiveselection
Exploration system Gahegan et al. 2002, Takatsuka and Gahegan 2002GeoVISTA Studio
Participants
Small number of participants: 6 Discount usability engineering
Nielsen 1994, Tobon 2002
The majority of the usability issues are detected with 3-5 participants.
cost & stafflimitations
Students of the International Master Programme in Geodesy and Geoinformatics at KTH
non-nativeEnglish speakers,fluent in English
nationality/mother tongue
Ghanian
Russian
SlovenianSpanish
Swedish
gender50/50
engineeringbackground
familiarwith GIS
voluntary participation
Not colour-blind
Experiment design
1. Introduction:- what the test was about, consent for using the data, etc.
Usabilitytest
in English
performed individually underobservation
1-1.5 h per participant5 steps
2. Background questionnaire:- gathering information on gender, mother tongue, background, etc.
3. Training: (unlimited time: ca. 45-50 min per participant)- introduction to data and visual data mining system- independent work though a script- questions allowed
4. Free exploration: (limited time: 15 min per participant)- whatever exploration in whatever way the participant wanted- no questions allowed- Verbal Protocol analysis – “thinking-aloud”- cooperative evaluation: if the participant stops talking, the observer can ask questions (“What are you trying to do?”, “What are you thinking now?”)
5. Rating questionnaire: - gathering information on participants’ opinion about the system- measuring perceived usefulness & learnability
The main part of the test
Results
1. Perceived usefulness & learnability
The bivariate matrix the easiest to use.
The map the easiest to understand.
The PCP the most difficult to understand and use.
2. Exploratory usability
Analysis of the thinking-aloud protocols
Hypothesesextraction
classificationacc. to source
backgroundknowledge
promptedby a visualpattern
refinement of aprevious hypothesis
Countingvisualisations total
frequencyrelativefrequency
Hypothesesclassification
backgroundknowledge
promptedby a visualpattern
Refinement of aprevious hypothesis
“Higher flowers probably havelonger leaves.”
“Are sepal length and sepalwidth correlated?”
“There seem to be twoclusters in each of these scatterplots.”
“Not only are there twoclusters, butthe bigcluster consists oftwo subclustersaccording topetal length.”
assign colour acc. to petal length.
“Flowers of the same speciesprobably grow in the same area.”
Visualisationfrequencies
Hypothesesgenerated
fR(i,j)=fT(i,j)/Nj
i – visualisationj – participant
Relative frequency:
Browse
Form ideasor hypotheses
Manipulate graphicsInterpret data
Amend initialidea according
to new information
Look for content
Look for content
Adjust browsing/decide where to look
Gatherevidence
Get new/moreinformation
Evaluateinitial idea
Adjust browsing/decide where to look
Tobon 2002
3. Exploration strategies Model of the visual investigation of data
3 groups mapping thestrategies
as paths
Browse
Form ideasor hypotheses
Manipulate graphicsInterpret data
Amend initialidea according
to new information
Look for content
Look for content
Adjust browsing/decide where to look
Gatherevidence
Get new/moreinformation
Evaluateinitial idea
Adjust browsing/decide where to look
Strategy no. 1:Confirm/reject a hypothesis based on background knowledge and then discard it. Repeat from the start.
Confirming a priori hypothesis
Browse
Form ideasor hypotheses
Manipulate graphicsInterpret data
Amend initialidea according
to new information
Look for content
Look for content
Adjust browsing/decide where to look
Gatherevidence
Get new/moreinformation
Evaluateinitial idea
Adjust browsing/decide where to look
Strategy no. 2: Form a hypothesis based on what you see, interpret and adapt it, confirm/reject it and discard it. Repeat from the start.
Confirming a hypothesis based on a visual pattern
Browse
Form ideasor hypotheses
Manipulate graphicsInterpret data
Amend initialidea according
to new information
Look for content
Look for content
Adjust browsing/decide where to look
Gatherevidence
Get new/moreinformation
Evaluateinitial idea
Adjust browsing/decide where to look
Strategy of group no. 3: Form a hypothesis based on what you see, explore further and adapt/refine it,according to what you see in other visualisations, confirm the refined version or adapt again and continue.
Seamless exploration
Small study size:- conclusions can not be too general, observations only
Conclusions
Training necessary:- new concepts visual data mining
unusual visualisations
interactivity of geoVISTA-based tools
Cooperative evaluation vs. strict thinking-aloud:- cooperative evaluation better (compared to a previous experiment)- no silent participants- easier to keep protocols
Discrepancy in perceived vs. actual learnability:- “PCP very difficult to understand”- PCP used most frequently of all visualisations- spaceFills almost never used
Exploration strategies:- three different exploration strategies
not related to gender
academic background
nationality/mother tongueGISexperience
Investigating spatial data visually is not so simple!
Substantial interpersonal differences in forming exploration strategies
Why? Question for the future
Thank you!