visualization of time-oriented...

WOLFGANG AiGNER visualization of time-oriented data 1

Wolfgang Aigner

aigner@ifs.tuwien.ac.athttp://ieg.ifs.tuwien.ac.at/~aigner/

wolfgang.aigner@donau-uni.ac.athttp://ike.donau-uni.ac.at/~aigner/

Version 3.214.12.2009

visualization oftime-oriented data

introduction

WOLFGANG AiGNER visualization of time-oriented data 2

Data types

1-dimensional

2-dimensional

3-dimensional

Temporal

Multi-dimensional

Tree

Network

= 4D space“the world we are living in”

[Shneiderman, 1996]

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Spatial + temporaldimensionsEvery data element we measure is related and

often only meaningful in context ofspace + time

Example: price of a computerwhere?

when?

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Differences betweenspace and timeSpace can be traversered “arbitrarily”

we can move back to where we came from

Time is unidirectionalwe can’t go back or forward in time

Humans have senses for perceiving spacevisually, touch

Humans don’t have senses for perceiving time

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…travel in timevirtually.

InteractivevisualizationGives us the ability to…

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Time-oriented data?

Event calendar

Snow height & sunshine hours

Organizationchart

iPod price

next >

WOLFGANG AiGNER visualization of time-oriented data 7^ up

Event calendar

WOLFGANG AiGNER visualization of time-oriented data 8^ up

Snow height &sunshine hours

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Organization chart

^ up

time

1998 2000 2002

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iPod price

^ up

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What is time?

“If no one asks me, I know.But if I wanted to explain it to one who asks me, I plainly donot know.”-- Augustinus (AD 354-430, The Confessions)

”Die Empfindung der Zeit hängt davon ab, auf welcher Seite

der geschlossenen Klotür man sich befindet.”-- Albert Einstein

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What is time-orienteddata?

no formal definition

what is considered as time-oriented data depends onthe intended task

a possible definition:

Data, where changes over time or

temporal aspects play a central role or are of interest.

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Visualization Design

data

task user

time domain

time-oriented data

visuali-zation

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Time domain overviewAdapted from [Frank, 1998]

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Scale

ordinalonly order is known

discreteevery element of time has a unique predecessor and successorcomparable to Integer

continuousbetween any two elements in time there might be another one

in betweendense timecomparable to Float

A B C

D

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Structure

linear

each element of time has aunique predecessor and aunique successor

cyclic

summer is before winter, butwinter is also before summer

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Viewpoints

ordered

multiple perspectives

branchingPast

Definite time - dataelement

assignment

PresentCurrently valid

state

FuturePlanning

Temporal uncertainty

Alternative scenarios

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Granularity

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Calendar

System of granularities and mappings between them

representational scheme

for human readability and usability

CalendarsGregorianAcademic (semester, trimester, ...)Financial (Quarters, Fiskal, ...)...

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Determinacy

determinatecomplete knowledge of temporal attributes

indeterminateincomplete knowledge of temporal attributes

no exact knowledge

i.e. “time when the earth was formed”

future planning

i.e. “it will take 2-3 weeks”

imprecise event times

i.e. “one or two days ago”

multiple granularities

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Time primitives

anchored

instant - single point in time

interval - duration between 2 instants

unanchored

span - duration of time

^ up

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Time-oriented data

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Visualization Design

data

task

visuali-zation

user

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Low-level TaskTaxonomy 1/2

Existence of a data elementDoes a data element exist at a specific time?Example: Was a measurement made in July, 1960?

Temporal locationWhen does a data element exist in time?Example: Is there a lecture taking place on November 24, 2005?

Time intervalHow long is the time span from beginning to end of the data element?Example: How long was the processing time for data set A?

Temporal textureHow often does a data element occur?Example: How often was Jane sick last year?

[McEachren, 1995]

[McEachren, 1995]

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Low-level TaskTaxonomy 2/2Rate of change

How fast is a data element changing or how much difference is there fromdata element to data element over time?

Example: How much did the price of gasoline change since last September?

SequenceIn what order do data elements appear?

Example: Did the explosion happen before or after the car accident?

SynchronizationDo data elements exist together?

Example: Is Jill’s birthday on Easter Monday this year?

[McEachren, 1995]

[McEachren, 1995]

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High-level TaskTaxonomy

Navigational Tasksnavigation in time or temporal datasearch (implies a specific user-defined target); browse

Observational Tasksdifferent characteristics of a single temporal historysearching for patterns; detecting disruptions and discontinuities; studying thedistribution of the data to identify concentrations of data (or classes of values)

Comparison Tasksrelating multiple temporal historiescomparing of two elements; rearranging; overlaying; studying correlation;searching for effects of causality; comparing evolution relative to a reference value

Manipulation Tasksmanipulation of data valuesvalue aggregation and segmentation

[Daassi, 2003]

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Visualization Design

data

task

visuali-zation

user

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Visual mapping of timeTime → Time (Animation)

probably the most natural form of mappingno “conversion” of concepts needed in betweenwell suited for

keeping track of changes

following trends and movements

not well suited for

analytic and explorative tasks

no direct comparison of parameters between different points in

time is possible

Time → Spacemapping of time to visual featuresdirect comparison of parameters between different points in time is

possible

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Visual variables

positionmost common mapping

the most accurately perceived visual feature

lengthsecond most accurate attribute

typically, the length of an object denotes the duration, asfor example in timelines

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Visual variablesangle, slope

analog-clock-based visualizations

connectionconnecting arrows or lines

“before element” --> “after element”

text, labelsimple text labelling

often combined with “connection”

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Visual variables

line (thickness)Increasing or decreasing with time

color (brightness, saturation, hue)brightness most appropriate

“fading away” against the background

transparency

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Visual variables

area

enclosure

size

texture

shape

less suited

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Visualization rootsStatistics

Visualization of time-series.

The time-series plot is the most frequently usedform of graphic design. [Tufte, 1983]

Mostly one parameter over time.

t

y

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Early time-series plot

Part of a text for monastery schools10th or 11th century (!)Inclinations of the planetary orbits over time800 years before other time-series plots appeared

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Train schedule

Paris to Lyon (1880s)