VISUALIZATION
- Cartography for the 21st century
Alan M.
MacEachren
Department of Geography
Pennsylvania State University, USA
Chair, ICA Commission on Visualization
e-mail: maceachren@psu.edu
and
the
ICA Commission on Visualization (1)
http://www.geog.psu.edu/ica/index.html
This
paper provides a brief overview of the evolution of Geographic Visualization
(GVis) and the activities of the ICA Commission on Visualization.
Initial research objectives for the Commission are detailed and a
draft research agenda being developed is outlined.
Proceedings
of the Polish Spatial Information Association conference, May, 1998,
Warsaw Poland
Cartography
has undergone profound change over the past decade. The change is stimulated
by a flood of new georeferenced data combined with new scientific and
societal demands and uses for these data along with rapidly evolving
geoinformation technologies. These technologies are part of wider developments
in information representation and processing with which they are becoming
increasingly linked (key among these are: geographic information systems
(GIS), visualization in scientific computing (ViSC), and virtual reality
(VR). One result of the links among cartography, GIS, and related visual
information technologies has been emergence of Geographic Visualization
(GVis) as a research focus and as a set of tools that promise to fundamentally
change (and enhance) the way scientists and others conceptualize and
explore georeferenced data, make decisions critical to society, and
learn about the world (MacEachren and Ganter 1990; Taylor 1991). While
GVis (like GIS) is an interdisciplinary endeavor, cartography is well
positioned to take a lead in advancing the frontier.
Approximately
a decade ago, a report to the U.S. National Science Foundation on
Visualization in Scientific Computing (ViSC) prompted a dramatic change
in the approach of science to visual analysis and visual evidence
(McCormick, et al. 1987). That report characterized visualization
as a method (and a product) that integrates of the power of digital
computers and human vision and directs the result toward facilitating
scientific insight.
Within
cartography and geography, the ViSC report prompted attention to the
role of maps and other visual displays in the process of science (DiBiase
1990) and an integration of the (then largely separate) research streams
directed to mapping technology and cognitive cartography (Buttenfield
and Ganter 1990; MacEachren and Ganter 1990; Taylor 1991). In 1993,
the International Cartographic Association Commission on Map Use formed
a working group on visualization to address implications of these
developments. A product of the first meeting of that group was a conceptual
model of map use (figure 1 - The (cartography)3 perspective on map
use) that emphasized an expanded view of use prompted by integration
of ViSC principles and cartographic representation methods (MacEachren,
1994). The expanded perspective on map use focused on three facets
of change in use: (1) in goals of map use (a shift from information
retrieval toward information exploration), (2) in target audience
for use (a shift from the general public toward individuals), and
(3) in flexibility of use (from inflexible static maps toward highly
manipulable dynamic maps).
The
implications of this model of an expanded map use space are, perhaps,
more apparent if we move to an even more abstract depiction of that
space--a 2D matrix that highlights the 8 corners of the cube (figure
2 - Examples of map use at the extremes of map use space). Virtually
all cartographic research, from the 50s through the 80s, that was
directed to use of maps is confined to one cell of the matrix--use
of static maps by individual "average" map readers to retrieve specific
information. Thus, not only did we know little about how highly interactive
computer interfaces influence the use (and usefulness) of maps (and
of other spatial representations), we had not explored the ways in
which static paper maps were used by experts as a prompt for visual
thinking. As a result, although we could (perhaps with some justification)
claim that the roots of scientific visualization are to be found in
geographic cartography (see Collins 1993), we were (in 1994) just
beginning to branch out from these roots.
Commission
on Visualization - initial research foci
In
1995, the International Cartographic Association approved formation
of a new Commission on Visualization?a Commission with a term running
through fall 1999, the eve of the next century. The Commission's focus
is on use of dynamic maps as prompts to thinking (dynamic maps are
maps that change in response to user action or to changes in data
to which they are linked). A variety of Commission activities over
the past three years have prompted an evolution of the (cartography)3
conceptual model of map use. The current model (figure 3 - A revised
view of map use space that incorporates DiBiaseís (1990) perspective
on the multiple roles of visualization in inquiry) deemphasizes the
tension between a communication and visualization approach to cartography
by treating GVis as a superset that includes attention to effective
presentation, but expands the bounds of geoinformation use well beyond
those traditionally considered within the purview of cartographic
communication (MacEachren and Kraak 1997). As outlined above, GVis
is a new rapidly evolving area of inquiry. While the focus of GVis
is certain to evolve, at this stage in development GVis can be defined
as a form of information visualization that emphasizes development
and assessment of visual methods designed to facilitate the exploration,
analysis, synthesis, and presentation of georeferenced information.
GVis has a combined emphasis on development of theory, tools, and
methods and on understanding how the tools and methods are used to
prompt thinking and facilitate decision making.
Initial
goals set for the ICA Commission on Visualization over its four year
term include pursuing a series of research priority areas that relate
to the expanded perspective on map use associated with GVis, a perspective
that includes an emphasis on highly interactive tools, used by experts,
in pursuit of unknowns. The specific research goals initially identified
are listed below, along with examples of research completed thus far
(in most cases by Commission members or those affiliated with the
Commission through its meetings and publications).
1.
Explore implications of the change from a cartography focused on optimal
maps toward one that emphasizes multiple perspectives (particularly
those multiple perspectives facilitated by direct manipulation interfaces
and by hypermedia methods). See Fernandes, et al (1997) and MacEachren,
et al (1997) for two perspectives on direct manipulation interfaces
and Cartwright (1997) for advances in the integration of multimedia
and visualization concepts in the development of multi-perspective
tools for exploring geoinformaiton.
2.
Develop a conceptual model and associated tools for depicting spatial-temporal
process information, with particular attention to links between dynamic
mapping and temporal GIS. See Kraak and MacEachren (1994) for a framework
through which to explore visualization of spatial data's temporal
component, Acevedo and Masuoka (1997) for issues associated with time-series
animation of urban growth, Buziek (1997) for consideration of human
perception as a factor in animation design, and Edsall and Peuquet
(1997) for consideration of temporal legends as controls for manipulating
both database queries and visual displays in temporal GIS.
3.
Develop a conceptual model and associated tools for the visualization
of data quality/reliability information. See Ehlschlaeger, et al (1997)
and Davis and Keller (1997) for work on modeling uncertainty and using
animation to depict multiple potential realities and Evans (1997)
for assessment of user comprehension of visualization and dynamic
methods for representing uncertainty.
4.
study methods for and implications of linking cartographic visualization
tools to GIS. See Rhyne (1997) for a conceptual approach to design
of integrated systems, Mitas, et al (1997) for work on the integration
of process models, GIS, and dynamic visualization for the study of
landscape processes, Qian, et. al (1997) for conceptualization of
operations common to GIS and GVis.
5.
Investigate the impact of exploratory spatial data analysis (ESDA)
methods on scientific thinking and hypothesis formulation along with
that of map-based spatial decision support tools on decision making
strategies and outcomes?as well as the impact of alternative computer
interface design strategies in both contexts. See MacEachren (1995)
for a theoretical perspective on the role of ESDA for science, Leitner
and Buttenfield (1996) for work on the role of reliability visualization
in a decision support context, and Howard and MacEachren (1996) for
a conceptual approach to interface/system design for GVis.
6.
Study the potential of three-dimensional representation tools and
the corresponding implications of both three-dimensional display and
the associated general trend toward realism (versus abstraction) in
scientific representation. Emphasis here has been on the first component,
particularly the application of VRML and related VR technology to
georeferenced data. See Fairbairn and Parsley (1997) for an introduction
to VRML for mapping and Neves, et al (1997) for consideration of the
use of GIS as a metaphor for immersive virtual worlds.
7.
Address implications, for our approaches to map design, of the ability
to link many representation forms together in hypermedia documents.
See Kraak and van Dreil (1997) for a conceptual approach to design
of hypermaps, Cartwright (1997) for development of metaphors to support
information access in a complex web environment of linked documents,
Aschedowne, et al (1997) for an approach to design of virtual atlases
that link information through the WWW, and Fabrikant and Buttenfield
(1997) for an approach to envisioning large data archives.
Commission
on Visualization - A GVis research agenda for the 21st century
Most
of the research cited above appeared in a special issue of Computers
&;Geoscience (May, 1997) or in the Proceedings of the June,
1997 ICA Conference in Stockholm. Just prior to that conference, the
Commission met for three days in Gävle, Sweden to concentrate
on developing a comprehensive research agenda designed to set research
priorities that will lead GVis into the 21st century. This research
agenda is still a work in progress and is presented as a draft outline
below. Details will be filled in over the next year.
Research
priorities are categorized under four themes that reflect several
aspects of visualization as an interaction between humans and computers
directed toward exploring and understanding geographic phenomena.
These four themes are outlined below. (2)
1.
Representation
Perhaps
the most obvious research focus for visualization of georeferenced
information involves issues of the visual display itself.
1.1
Extending the object of representation
It
is clear that the integration of ViSC and VR tools with cartographic
tools extends the object(s) of geographic representation in various
ways. Some of these ways were identified in initial goals of the commission:
the representation of space time phenomena and processes and the representation
of data reliability. To this list, a need has been identified to develop
methods for the visualization of algorithms used to process spatial
data, the visualization of data structures and query processes, and
the application of GVis methods to spatialization of information in
general (i.e., of non-spatial information).
1.2
Extending forms of representation
As
a complement to extending the range of objects to which GVis methods
are applied, substantial research effort must be directed to taking
advantages of advances in computer graphics that make the new forms
of representation possible. Much of the initial GVis research has
concentrated on adding dynamic components to traditional 2D and 2.5D
representational forms (e.g., animated planimetric maps and flythroughs
of perspective views). Priority areas identified for research emphasize
two developments, the rapid increase in computer power that makes
dynamic manipulation of map parameters possible and the increasing
availability of tools for building virtual environments. Research
is needed to determine how to integrate methods for dynamic manipulation
into GVis tools (e.g., to merge exploratory data analysis methods
with map animation) and to integrate VR technology with geographic
data and principles of geographic representation (e.g., adding geofunctions
to VRML or using immersive VR to explore abstract georeferenced data,
such as output from a global climate model).
In
addition to research on the technical problems of using new technology
to best advantage, research is also needed to consider the implications
of new representation forms. Questions here relate to the semiotics
of extended representational environments, the relative merits of
abstract versus realistic representations, and what the concept of
representation means in a virtual world. One component of an approach
to addressing these questions involves considering cognitive aspects
of visualization tool use (detailed below). In addition, these questions
can (and should) be approached from the perspective of the philosophy
and sociology of science.
2.
Interface design
The
Commission has, from the start, directed attention to extending cartographic
principles, developed for static maps, into the realm of dynamic maps
and related displays. In addition to research focused on what and
how we represent georeferenced information, therefore, attention must
also be directed to mechanisms we provide that allow users to interact
with those representations. Research priorities identified here relate
to the following:
2.1
Typology of visualization operations
Cartographers
have directed considerable attention to developing typologies of variables
used in visual (and tactual and sonic) geographic representation and
guidelines about appropriate use of those variables. To develop a
coordinated approach to interaction with manipulable maps, however,
it is essential that a complementary typology of visualization operations
be developed. A step in this direction is a typology proposed by Keller
and Keller (1992), but that typology does not focus specifically on
visualization of georeferenced information, nor does it consider the
need to integrate visualization operations with query operations in
the context of GIS-GVis integration (see below).
2.2
Controls for operations
Interactive
displays of georeferenced information require development of controls
through which users can interact. Although there are many basic tools
generally available that can be adapted for use in GVis environments
(e.g, buttons, sliders, etc.), there has been no systematic attempt
to develop a typology of control forms for manipulation of spatiotemporal
information. Developing such a typology could lead to more consistent
interfaces for geoinformation processing environments and more logical
matches between operations and controls.
2.3
Facilitating information access in complex hyperlinked information
archives
As
the World Wide Web and related technologies provide a mechanism to
link geoinformation in complex ways, there is a critical need for
research directed to methods that facilitate navigation through that
web of information. Potentially productive approaches involve the
development of appropriate metaphors for navigation in these complex
information spaces and the spatialization of non-spatial information
as a method to identify relationships among information objects.
2.4
Intelligent GeoAgents
An
intelligent GeoAgent can be defined as a virtual entity that understands
our needs and prefrences related to geographic data access and/or
its analysis and representation. Intelligent GeoAgents should act
as filters and interpreters of information and contexts. One potential
role for intelligent GeoAgents involves embedding cartographic expertise
within database objects to be displayed. Each object could be bound
with a GeoAgent that evaluates the context of use and the display
context within which the object finds itself, and select a display
form accordingly. Another role for GeoAgents is as information seekers
that search the web for information that meets criteria of a fuzzy
query. The GeoAgent would adjust to the information context it finds
itself in, adapting the query parameters in response to such things
as links found among information objects, density of information in
particular locations within attribute space, or simply success at
matching the initial query.
2.5
Collaborative visualization
An
emerging area of research in ViSC generally is collaborative visualization--the
development of environments that facilitate the use of manipulable
visual displays for exploration of ideas and/or decision making by
two or more individuals (perhaps located at a distance). Tools for
collaborative visualization of georeferenced information have considerable
potential for use in contexts such as urban planning, environmental
management, and scientific interpretation of models of climate or
other environmental processes.
3.
Database-visualization links
One
of the most common arguments for developing visualization tools is
that such tools can help us cope with the rapidly increasing volume
of information being generated by our information society. This potential
can only be realized in the case of GVis, however, if GVis is integrated
with other technologies for storage, access and analysis of that georeferenced
information. Three key research priorities are identified in this
context.
3.1
GIS?GVis integration
Traditional
GIS environments have treated visual display as an output, thus an
endpoint of a query or analysis process. GVis, on the other hand emphasizes
information exploration and hypothesis generation, thus it is as likely
to produce queries as be the result of one. For GVis to reach
its potential, a new view of both GIS and GVis system design is required.
Research must address the range of issues associated with merging
the goals and functions of GIS and GVis.
3.2
Spatial data mining?GVis integration
As
data volumes continue to increase, methods of "mining" data are being
developed to sift through the vast amount of information in a search
for interesting patterns and relationships. Visualization has a potential
role at all stages of the data mining process (from preprocessing
and error identification through selection of information to be mined,
to interpretation of results from data mining). For georeferenced
information, this integration of GVis in the data mining process will
require, not only adaptation of approaches to data mining that recognize
the unique properties of spatial information, but the adaptation of
GIS tools to facilitate the application of both GVis and data mining
methods.
3.3
Generalization and Visualization
Research
priorities discussed under this theme were prompted by a joint session
of the Commission on Visualization and the Working Group on Generalization
that took place in Gävle, Sweden, June, 1997. Many applications
of GVis require a facility to change spatial or temporal scale. Dynamic
visualization offers several new challenges for research in generalization.
One is to develop methods for making effective use of the level of
detail node in VRML, in order to achieve an appearance of seamless
change in scale--a problem that requires adapting many generalization
concepts developed for 2D maps to 3D worlds. Similarly, the emphasis
on spatiotemporal information characteristic of many GVis applications
creates a need to begin to address issues in spatiotemporal generalization.
A third generalization issue needing attention involves the generalization
of hyperlinked networks of information. Just as a base map with too
much detail can impede visual analysis of thematic information superimposed
on that base, a too detailed network of links among information objects
can impede visual exploration, searching, or decision making based
on that network of information. Methods to generalize these networks
are needed. Cartographic generalization is, of course, an active research
area in its own right replete with many unanswered questions. One
avenue of GVis research with potential to support advances in generalization
research involves the use of GVis methods to facilitate understanding
of the generalization process.
4.
Cognitive aspects of visualization tool use
The
promise of visualization is based on an assumption that human vision
and cognition has powerful information synthesis and pattern seeking
capabilities that can effectively complement the raw information processing
power of digital computers. Harnessing this power of vision, however,
requires developing a more complete understanding of spatial cognition
and perception of visual displays. While we have a solid base of knowledge
about perception and cognition as it relates to static paper maps,
we know much less about the cognitive and perceptual issues associated
with 3D and dynamic displays. Seven priority topics are identified
here.
4.1
Cognitive aspects of dynamic representation
Our
knowledge of cognition related to dynamic scenes (even real world
scenes) is limited. Key questions relate to issues such as the role
of animation in understanding process, the implications of various
parameters of an animation (e.g., display changes per second, smoothness
of transition between frames, etc.) on that understanding, differences
in cognitive processing required to interpret temporal versus nontemporal
animation, and methods of retaining orientation in flythroughs.
4.2
3D representation and virtuality
As
technology makes it possible to create increasingly realistic representations
of the geographic environment, it is important to consider the cognitive
implications of this realism. Questions to be addressed include the
cognitive processes involved in identifying the correspondence between
2D (planimetric) representations and 3D representation, exploring
the changing relationship between sign-vehicles and referents as representations
become increasingly realistic, and developing and understanding of
the integration of visual and sonic information in the context of
immersive and non-immersive virtual worlds.
4.3
Schemata, metaphors, and human-computer interaction
Facilitating
human-computer interaction requires development of logical approaches
to interface design and the creation of appropriate interface controls
that allow users to manipulate parameters of the display. Also required,
however, is a comprehensive understanding of the cognitive aspects
of interaction with the display. Do, for example, different control
forms (e.g., a time wheel versus a time line) prompt different knowledge
schemata that result in different interpretations of what is seen?
A similar question involves the implications of possible interface
metaphors for the strategies that a user takes to data exploration
and the interpretation of results from that exploration.
4.4
Hypermedia navigation
The
web is a complex maze of information in which users frequently are
frustrated in their efforts to locate the information they require.
Attention to cognitive aspects of wayfinding in this information environment
is needed as a complement to research (discussed above) directed to
design of interface tools that facilitate information browsing. One
potentially fruitful avenue of research is to explore the transferability
of conceptual models of wayfinding in real spaces to wayfinding in
information spaces. An additional topic to investigate involves strategies
used to maintain orientation and context in multidimensional information
spaces.
4.5
Expert-novice distinctions
At
issue here is the impact of expertise on use of GVis and differences
in design strategies that should be developed for GVis users with
differing kinds or levels of expertise. At least two forms of expertise
must be considered, that in the technology being used and that in
the domain of knowledge to which the technology is applied. A better
understanding of expert strategies for the application of GVis tools
to data exploration or problem solving could be used to design knowledge-based
GVis tools that prompt novices to use expert strategies.
4.6
Influence of GVis methods on the scientific process / scientific understanding
There
is an implicit assumption behind ViSC that visualization will facilitate
science. While anecdotal evidence may seem to support this contention,
anecdotal evidence by its nature is generally positive. There is little
systematically collected empirical evidence to either support or refute
the claim and we know relatively little about how scientists actually
use sophisticated visualization tools and methods. Research is required
to test the underlying assumption that GVis facilitates science and
to develop an understanding of the implications for science of visual
geographic representation methods.
4.7
Role of visualization in decision-making
The
primary question here is whether GVis tools change how decisions are
arrived at and/or the outcome of decisions. Assuming that some changes
are produced, it is important to explore the nature of those changes
and whether decisions are more consistent or otherwise "better." Additional
questions to address include the implications of various components
of a GVis environment on decision making (e.g., the kinds of information
displays provided, the kinds of interaction allowed, etc.) and the
role of data reliability visualization on strategies taken to decision
making.
1 This
paper discusses the evolution of geographic visualization as an area
of research and application affiliated with cartography. Emphasis
is placed on work of the International Cartographic Association Commission
on Visualization (chair: Alan M. MacEachren; co-chair: Menno-Jan Kraak)
and on a draft research agenda being developed by the Commission.
The Commission activities, particularly the developing research agenda
are joint activities of the full and corresponding members of the
Commission. Thus, the Commission as a whole should be considered (and
is listed as) a co-author of this paper--but this does not imply that
all Commission members agree with ideas presented here.
2 References
are omitted from this draft, but that omission should not be interpreted
as an indication that no progress has yet been made. In most cases,
there is at least a preliminary base upon which to build (in some
cases, research already cited above provides this base). A discussion
of relevant research associated with each theme will be included in
the expanded research agenda document.
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