Organisation

March

PhD defence Ms Irma Kveladze

Department of Geo-Information Processing

Irma Kveladze_web

Title of defence

Space-Time Cube - Design and Usability

Summary

Over the past decades, we have witnessed increasing achievements of technology that affected the lifestyle of modern society. Wide availability of inexpensive navigation equipment (mobile phones, digital navigation devices, GPS receivers) enables the collection of information on movements more easy than ever before. These recordings provide accurate location (latitude, longitude, altitude), time and attribute information about objects (humans, animals, vehicles, etc.) anywhere in the world. This information on change in space and time is the study interest of experts in various research domains.

Nowadays, a wide range of visual methods as well as interactive techniques, supported by computational algorithms has been developed to support the process of exploration of complex movement datasets. One of these graphics is the Space-Time Cube (STC), which has the ability to model and represent relationships between movement patterns over space and time. The two-dimensional horizontal plane (x, y) represents the location of an object in space and the vertical plane (t) represents its location in time. St-path represents the movement through space-time undertaken by an object. The "shape" of the trajectory contains information on the nature of the movement. It can answer questions about the where (locations) and when (time), but also about ‘how long’ and ‘how fast’.

The idea of the STC originates from the concept of Time Geography introduced at the end of the seventies of the last century by the Swedish geographer Hägerstrand for studying the spatio-temporal characteristics of human activities. By that time, it was an analytical framework for the exploration of spatio-temporal interactions in people’s everyday lives. Until the beginning of this century, the model was used sparsely in studies in human geography. The reason for this was the poor computational development causing tedious manual drawing and data collection. Later on, technological achievements in Geographical Information Systems (GIS) made the implementation of time geography easier. Clearly, in scientific research, space-time movements acquired significant interest of researchers, and scientists renewed their interest in time geography. Nowadays, a wide range of topics such as migration, gender studies, travel behaviour, archaeology, history, transport accessibility, etc. have accumulated complex movement datasets that require visualization in order to accommodate the extraction of knowledge. For this purpose, the STC is a widely used visual representation.
However, little is known whether the cube is truly efficient and effective to satisfactorily display complex datasets as stand-alone visual representation or as a part of a GeoVisual Analytics (GVA) environment. Earlier usability research did not offer directions on how the STC content should be designed from a cartographic perspective, or whether it is influencing the exploration process. The lack of such evaluation studies for the STC to visualize data is the main driver of this research.

The focus of this research is on the development of effective and efficient visualization strategies and design guidelines through systematic usability studies in specially construct GVA environments to facilitate knowledge extraction from various datasets. To be able to realize this goal, the research is divided in three main objectives.

The first objective is a systematic investigation of relevant research on time geography, geovisualization and usability disciplines to highlight knowledge in theoretical and practical studies.

The second objective is to develop a conceptual framework based on objective 1’s findings, by incorporating problem, solution, and evaluation perspectives resulting in the design guidelines and visualization strategies. This offers an approach to the evaluation of the STC content with special attention for cartographic design aspects and the environment in which the STC has to function. The cartographic design guidelines are linked to suggested visualization strategies and allowed the development of hypotheses for extensive usability studies. These systematic studies had to identify the strengths and weaknesses of the STC under different conditions.

The third objective concerns the evaluation. During the evaluation, four test datasets in varying size and complexity (see Figure a, b, c, d) based on the real world problems in close cooperation with the owners, the domain experts have been used. Combinations of different qualitative and quantitative usability methods have been used. The first allows one to examine people’s experiences, actions, behaviour, etc. in detail since it provides complex descriptions of experiences gain during the experiment. Methods include video/audio/screen recordings, think aloud, observation and post experience interviews, and focus group discussions. The second intends to measure, quantify and count research issues identified during a usability study. Methods include task analysis, eye tracking, and pre-selection questionnaire.

The evaluation has been split in six phases. The first phase starts from the problem perspective based on the requirement of domain experts. To realize the research goals a User Centred Design (UCD) research methodology was followed. The second phase links to a solution perspective and is based on theoretical visualization knowledge.

The third phase included two experiments designed for and executed in the working environment of the domain experts at their home universities. The objective of the experiments was to gain deeper insight into the further needs and experiences of the domain experts to potentially extend and improve the STC application. Thus, by measuring and studying confusions, disorientations, satisfactions and success of their activities during the interaction with the application as well as the expectations they expressed, the requirements for the design and tools were identified.

In the fourth phase the experiment’s objective was to obtain information on the cartographic design aspects for the STC content. It reports on the results of a usability study conducted with nine experts from the geovisualization domain. A focus group experiment was the starting point for a discussion on the use of the design alternatives hypothesized earlier (see Figure e). The experts from the geovisualization domain judged the suitability of the different design. The results reveal that the use of these design alternatives is influenced by the size of the data sets used. Nevertheless, color hue and color saturation were advised as the most suitable solutions for data visualization. However, at the same time remarks were made that only design will not be able to deal with the exploration of such datasets and that additional analytical functionality is just as important.

Phase 5 consisted of a usability study of design alternatives with the stand alone STC was done via a task-based experiment with 22 participants who were unfamiliar with the cube. During this experiment, participants were asked to think aloud while executing the given tasks. This process was video/audio/screen/eye recorded by Tobii Studio software. After completing the tasks, the participants were interviewed to share their opinions, attitudes and experience gathered during the experiment. The materials derived from these qualitative experiments, resulted in a transcript protocol, and the outcomes derived from eye tracking (see Figure f) and task execution resulted in quantitative metrics. The outcome of the experiment revealed various reasons for the acceptance or rejection of the design options. The results coincided with what the geovisualization experts suggested during the focus group evaluation. The experiment conducted in phase five, revealed a clear preference for the visual variable color to visualise different types of data complexity in the STC. The perceptual properties of visual variables worked as predicted with the exception of size.  Size is known as the only visual variable with three perceptual properties, but this experiment could only partly confirm its selective perceptual characteristics.

Finally, in phase six the STC was judged in three different GVA environments each with its own data sets, incorporating the results of the earlier phases. Next to the STC the participants could work with a 2D map, a parallel coordinate plot, the time wave and a time graph. The task- based experiments employed a mix of qualitative and quantitative user research techniques. Similar to the previous experiments, test participants were asked to think aloud while executing tasks. After completing the tasks, the participants were interviewed to derive more information on their experiences during the experiment. The qualitative studies resulted in a transcript protocol, and the eye tracking (see Figure g) and task execution resulted in quantitative efficiency metrics. The results of the analysis show that the appreciation for each of the visual representations available in the GVA environment differs depending on the data and environment. In conclusion, the positioning of the STC in various GVA environments offers better exploration options and a better understanding of temporal events, multiple data characteristics and the geography.

This research contributes to Time Geography in general and the usability of the STC in particular. The value of the STC as an elementary part of Time Geography to get insight in all kinds of movement data has been proven by using four different case studies in this research. The usability of the STC has not only been studied as a stand-alone visual representation, but has been placed in the context of GeoVisual Analytics environments with other (carto)graphic representations.

The research confirms the importance of the harmonious coexistence of cartographic design theory and visualization strategy. The empirical investigation of cartographic design aspects confirmed the expected influence of data complexity on design options for the STC. In such situations a simple design is preferred. The known perceptual properties of the visual variables proved to be valid in the STC as well, with some minor deviations and a high preference for color. The research also demonstrates that the STC functions well in GeoVisual Analytics environments.

Figures: Four use case studies used in this research: a) Travel log data: Estonia; b) Historical event: Napoleon’s Russian Campaign; c) Pedestrian movements in Delft city center; d) Passive mobile phone positioning data of commuters, Tallinn. The STC applications were created using Udig with a STC plug-inn (a) and ILWIS (b, c, & d). The last package is the current development platform and can be downloaded from http://52north.org/downloads/ilwis. e) Focus group interview discussion on visual variables. f) Example of the HeatMap generated from eye movement behavior of the participants during task execution process. g) Example of the GazePlot generated from eye movement behavior of the test participants during task execution.

 

Biography

Irma Kveladze graduated from I. Javakhishvili Tbilisi State University (TSU) of Georgia, at Faculty of Geography and Geology her BSc and MSc degree in Cartography, Geodesy and Geo-Informatics. During her MSc study, she worked as a researcher in Georgian - German joint study project “Establishment of a scientific working group on livestock induced effects on nature in Georgia”. Prior to the PhD project, she worked as a GIS assistant at the Caucasian office of World Wide Fund for Nature (WWF), and at Caucasian Institute of Mineral Recourses (CIMR) as Engineer (GIS specialist). At the same time, she was co-founder and member of the administrative board of the international environmental organization – Caucasus Research Centre (CRC). From work experience, she developed an interest in how cartography and geovisualization innovate effective visualization methods to explore dynamical changes in various geographic phenomena. From 2009 she started working on her PhD project in the research program Spatio-Temporal Analytics, Maps and Processing (STAMP) on the topic: Space-Time Cube, Design and Usability at Faculty of Geo-Information Science and Earth Observation (ITC). She is currently working on research project with human geographers at University of Tartu to investigate ethnic segregations in Estonia.  

Kveladze, I., Kraak, M.J. (promoter) and van Elzakker, C.P.J.M. (co-promoter)  (2015) Space - time cube design and usability. Enschede, University of Twente Faculty of Geo-Information and Earth Observation (ITC), 2015. ITC Dissertation 268, ISBN: 978-90-365-3859-6.

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Timesheet
Event starts: Wednesday 18 March 2015 at 14:30
Venue: ITC Auditorium
City where event takes place: Enschede

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