A City Metaphor to Support Navigation in Complex Information Spaces Andreas Dieberger Emory University - Multimedia Communications 550 Asbury Circle Atlanta, GA 30322, USA email:
[email protected],
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Abstract A major problem for users of modern information systems is the retrieval of new and previously viewed information from the system. Systems like the Word-Wide Web are heavily interlinked but do not communicate structure that helps users to navigate the information it contains. The use of appropriate navigation metaphors can help to make the structure of modern information systems easier to understand, and therefore, easier to use. We propose a conceptual user interface metaphor based on the structure of a city. Cities are very complex spatial environments and yet, people are used to navigating within cities. They know how to get information, how to reach particular destinations, and how to make use of the infrastructure. Furthermore, cities possess a unique set of navigational tools that lend themselves to creating sub-metaphors. A city metaphor makes this existing knowledge about a structured environment available to the user of a computerized information system. In this paper, we first describe properties of future user interfaces (or user interface metaphors) that we think will distinguish them from current systems, like the richness of information or the use of visualizations to show the structure of information spaces, and the ability to serve not only a single user, but a user community. Then we describe the structure of the information city metaphor, its structuring and navigation metaphors, and what we see as its main advantages and disadvantages.
1. Introduction Users of modern information systems often struggle to retrieve and to re-find information they have seen before. Challenges navigating such systems as the Word Wide Web for example arise from the lack of apparent structure. Using appropriate navigation metaphors, we make the structure easier to understand, and therefore easier to use. User interfaces are based on metaphors that help understanding the system in terms of concepts the users already know. Spatial metaphors try to exploit the extraordinary human ability to organize objects in space, to recall and reason about their locations, and many other space related cognitive abilities [25]. We can extend the space of the commonly used desktop metaphor to rooms, buildings and a whole city. The city structure is interesting because its enclosed spaces can represent levels of enclosure or security -- a necessity for modern information systems. In this paper, we describe a spatial user interface metaphor. It is called the Information City , and is a conceptual system focused on navigation. The city concept further
provides metaphors for security and privacy. Cities are social spaces: people guide each other, point out landmarks, give route descriptions, and interact directly with each other. These properties of the city environment and its navigational infrastructure are the qualities we try to capture in our Information City metaphor to transfer them into the domain of virtual information spaces. Structure of this Paper In Section 2 we argue that communicating the structure of an information space is essential for navigation, and define navigation as a mapping from knowledge about the environment to activities in it. We then further describe spatial metaphors to include two concepts that can help remedy some of the problems of spatial metaphors: history enriched environments and magic features. We further motivate our choice of the city metaphor, and describe the basic concepts for the metaphor. Section 3 describes the Information City in more detail. We define structural elements as a basis for navigational tools. Information carrying entities provide information within the city structure, and magic features help improve the metaphor’s scaling behavior. Section 4 addresses a few issues an implementation of the metaphor will face, and Section 5 draws conclusions from the previous sections, points out unresolved issues, and summarizes the paper.
2. Spatial Metaphors for Navigation within Complex Information Spaces Finding information in an information space can be supported by an appropriate user interface metaphor, as it fosters understanding of the information space’s structure. Information spaces need structure to be useful and this structure needs to be communicated to the user. The term information space hints at a spatial conceptualization of the underlying metaphor. There is a strong relationship between spatial metaphors and information visualization: the visualization communicates the structure of the information space to the user which makes navigation in the space possible. 2.1. Basics for navigation Information Visualization The information space’s structure can be communicated to the user through a graphical representation of the space and the elements in it 1. Examples of such visualizations are the Information Visualizer [8], the Navigational View Builder [32], the Narcissus system [19] Chalmer’s landscape metaphor [9], or the visualizations for the Hyperwave system [3].
1
We use the term visualization, but want to stress that the representation of structure not necessarily has to be visual.
All of these visualizations are based on spatial metaphors. While the metaphor is not always made explicit, it influences the visual design of the system. Even without explicit spatial structure in the data set, it is sometimes useful to represent data using spatial metaphors, or to talk about the structure in spatial terms. Generally, it is assumed that spatial visualizations of information structures help users to learn the structure of the information space.2 Navigation in Information Spaces Many information systems contain information with hypertext properties [33]. Hypertext consists of nodes containing information connected by links. Users navigate this structure by following (directed) links. Where most types of information have a typical order in which they should be apprehended, this is not necessarily true for hypertext. Users easily lose orientation even in small hypertexts. This has been called the getting lost in hyperspace problem. It is not a shortcoming of the hypertext concept so much as it is the failure of the hypertext’s user interface to communicate the structure of the information to the user [14]. Users map from the information space's structure and their tasks to navigational activities. This mapping is impossible without apparent structure. This becomes apparent in the key questions of (information) navigation [12]: •
"Is there 'a piece of information' with the property X?"
•
"How do I get to this information?"
• "Where am I now in relation to ...?" The spatial formulation of these questions indicates a spatial conception of the navigation process. Note that users do not inhabit a position in space and have a history of visited places unless the user interface provides it. 2.2. Spatial User Interface Metaphors The usefulness of spatial metaphors is intuitively understandable and proven in several studies, like [4]. Two earlier studies are [24, 30]. However spatial metaphors do have their shortcomings which need to be addressed to make them the basis of an information system. An advantage of spatial organization schemes is the user’s initial familiarity with them. Most people organize objects in a spatial way, and have strongly developed spatial cognitive abilities. They have highly developed methods to describe access paths to objects, and are able to understand and follow route descriptions even when these are incomplete or partly incorrect. Spatial arrangements can express relationships between objects that are difficult to describe in a formal way, and spatial language can describe complex relationships or even leave room for ambiguity. 2
It is often assumed that visualizations are the better the more 3-dimensional they are. However Poblete reports in [34] that simpler and flatter representation of information structures sometimes are learnt easier than more advanced 3D visualizations.
A good example for complex spatial relationships is the structure of a city as overlapping neighborhoods or districts. City areas do not form a strict hierarchy, but rather, a structure of partial containment [1]. At the same time, the city structure shows hierarchical properties which promote further understanding. The major shortcoming of spatial metaphors is that they scale up badly. The desktop metaphor is an example of this. Many users choose to view their files as a list rather than as a spatial arrangement of objects because a large number of objects cannot be represented well. This shows the close relationship between spatial metaphors and information visualization because a more elaborate visualization of the file space, like the Cone Trees of the Information Visualizer, scales up much better [8]. The city metaphor addresses scaling by providing global overviews in the form of city maps. People may be familiar with only a limited part of a city, but have strategies to navigate unknown parts reasonably well by using either maps and available infrastructure, or by interacting with other people. This reduces the apparent size of the city and thus, also addresses the scaling problem. The “magic features” we introduce into the city provide an additional tool to cope with the complexity of very large spaces. The Necessary Amount of Realism Spatial filing is a useful form of organization for many tasks that involve a large mass of diverse objects or entities. The key word here is diverse because spatial filing does not work well when the objects look too similar. Representing the space and the objects in it realistically helps create the necessary diversity. A detailed rendering of the metaphor’s source domain eases transfer of preexisting knowledge to the target domain. Artificial environments can be enriched by visualizing, for example, usage information as read wear [21]. The idea behind history enriched objects is that they wear out like real objects, and that visualizing usage of information highlights frequently used and therefore more promising objects. For examples of recent work on group memories and collaborative navigation that often make use of concepts like read wear, see [20, 31, 35]. Information richness in systems that support collaboration and interaction between users is an important ingredient to provide what we call social navigation [16]. Social navigation is a behavior where users of information systems freely share pointers to information, and help out other users who are disoriented or new to the system. Essentially social navigation is something that happens in every inhabited city space as well, when people ask for the way or when inhabitants modify their environment to make it nicer, more personalized and therefore, easier to recognize and navigate. Such information in the world is created by the inhabitants of a city, and may actually be incomprehensible to outsiders. Information of this kind is close to Bolter’s Writing on the world concept [6, 12]. Current information systems seldom support user communities that can personalize the information space in such a way, but in a city metaphor, it would be the logical thing to support such processes to make the environment more legible [28]. Note that this use of the word “legible” differs a little from the concept of “legibility” as used in [29], where it refers to how easy it is to read and learn an overall city structure.
Magic Features -- Deliberately Breaking the Metaphor Spatial organization is no universal cure for navigation issues. Spatial arrangement determines both the distance as well as the effort to cross this distance between objects. In conventional space, effort is proportional to distance, and available navigational means. Information systems that slow down navigation just to convey the feeling of distance probably will not be accepted well once distances and delays reach a certain amount.3 We therefore need to provide shortcuts through space that may break the relationship between distance and effort in favor of navigation speed, and appear as something that lies outside the underlying metaphor. We call them magic features [12, 13]. A consistent spatial metaphor seems to prohibit the use of magic features, however, by loosening the rules we can improve navigation in the information space. This has to happen in a controlled manner -- otherwise the spatial metaphor becomes too confusing for the user. Magic features should be designed to look differently enough from the rest of the system so that users recognize them as something special [13]. They can provide shortcuts that can make navigation in large spaces more effective, and thus tackle scaling issues. 2.3. Motivation and Basic Concepts for the Information City The main argument for using a city metaphor is that cities provide structures that scale up relatively well and provide navigation tools to cope with the space's complexity. Another argument for the city is that people know strategies to navigate effectively in unknown parts of the city. Although cities are hierarchical in one sense, people's mental representations of cities also contain also overlapping elements. Based on these elements, we can describe complex relationships of containment in a city metaphor, including encapsulation and access control. In addition people are used to navigating city structures, and to interacting with other people in the city environment. They know social protocols that control the interaction with other users when inquiring about locations, asking for the way, or gaining access to closed spaces. The city is, therefore, also a social space. 2.3.1. Elements of the City Environment When people navigate within a city they build a mental representation of it that they use to reason about the environment. According to Kevin Lynch's study "The image of the city" [29] there are five major elements in that city image: the Node, the Path, the Edge, the District and the Landmark.. Note that these are not the only city elements conceivable (see for example [26]).
3
In an early version of the Storyspace hypertext system such delays occurred for technical reasons when accessing nodes that were ‘far away’ in hyperspace. Accoring to the authors (personal communication) users noticed and appreciated this additional navigational feedback.
A path is one of the two linear elements in the city environment. It describes how to get from point A to point B, for example, from the home to the office. Paths can cooccur with major streets in the environment, but they do not have to. Districts are areas containing objects showing common character. This may be in the style of buildings, their prominent use, or any other aspect. Districts are not necessarily clear-cut entities. An alternative term is neighborhood. Landmarks show unmistakable form, and are discernible from all similar objects in the environment. Landmarks are of special importance when giving directions since they are easily recognizable. The node is another point-like element, and the edge is a linear separating element. A well-designed real city provides a well-balanced combination of these city elements. This allows users to easily learn paths, to describe and remember routes as well as locations. In Lynch’s words, it makes the city more legible [29]. A legible environment is easier to understand and to learn. It also may give locations within the city a feeling of place which provides context for objects nearby, and a framework for social interaction [17]. In our design of the Information City metaphor we therefore tried to provide a reasonable mix of characteristic city elements so that users can easily learn the environment. Richness of the Environment and Magic Features City elements must be visually different enough to be identifiable. In real cities this is taken care of through building styles, facade ornaments, including personalization by the inhabitants (see above) and so forth. In a digital city, we have to artificially create such diversity. Ideally, this not only makes elements of the city easy to distinguish, but also conveys information to the user. To improve scaling of the city metaphor, we define magic features as shortcuts through the city environment. They can be magic portals or transportation that is always available. They appear also in structures like a room that contains an area that is larger than its outside (envelope structure). Note that magic features should be used sparingly. Creating too many magic portals, for example, destroys the specialty value of these elements. Users will not see them as an addition to the structural elements of the city but as the main structure. The result is a hypertext of buildings without the structural benefits of the city metaphor. 2.3.2. Other City-like Metaphors Several spatial metaphors in literature have been based on the structures found in buildings and cities. The desktop metaphor is a subset of such a concept itself. Extensions of the desktop can be found in systems like Magic Cap or the Xerox Rooms systems [18]. Further extensions can be seen in systems like the Digital City (http://www.viper.net/fun/dc), the WebWorld (a discontinued system on the WorldWide Web), the Paxton virtual city (http://www.eolas.co.uk/mellanta/fd/) or Apple’s discontinued e-World, all of which use village or city metaphors. Recent systems
extend the spatial metaphor to a multi-user VR world to meet people and to chat, like the Worlds Chat system (http://www.worlds.net/). Through advances in the field of information visualization, there is a growing interest in city-like metaphors. For an example, see the visualizations for the HyperWave system, a second generation distributed hypertext system that shows many advantages over the architecture of the World Wide Web, and could be used as a template for creating city structures for the Web as well (see [2, 3]). Most of these systems present the user with a relatively small space in which she can arrange objects according to her wishes, but do not scale well as their metaphors often add only metaphorical sugar to an existing system. In systems designed mainly as meeting spaces, navigation of large amounts of information is a minor concern, and therefore, only limited design effort is spent on these issues. Some systems do not directly use a city metaphor, but rather, apply city-planning principles to improve a visualization technique. A good example is Rob Ingram’s work. His LEADS system improves the legibility of an information visualization by identifying districts, paths and nodes in the visualization, and by providing landmarks [22, 23]. Like our city metaphor, this system is geared towards both an information space that is relatively static, and users who frequently revisit the space, because otherwise, there is no point in learning the space’s structure.
3. Description of the Information City Metaphor In this section we describe the Information City metaphor. Because of space constraints the ontology described here is only a part of the metaphor. For more details see [12]. We start with the structural framework as the basis for the navigation tools. Information content is provided though information providing elements. To improve the scaling properties of the city we introduce several magic features. In an additional section we discuss issues of actually creating an Information City. 3.1. Topology and Overall Structure The topology of the Information City is based on generalizations of Lynchs’s three major elements: container, landmark and path. The Information City consists basically of a collection of containing elements that are associated with at least one landmark. The largest containing element is the city itself, but there is no restriction to only one city. The next smaller element is the district. Inside districts there may be sub-districts that consist of buildings. Buildings contain floors and rooms -- according to the structure of the information organized within the container. Each container can be considered a complete subspace that does not have to adhere to the general city framework but may be organized using a different metaphor, should that be adequate.
3.2. Lesser Structural Elements When closing in on the city, major navigational paths that separate large districts come into view first. As districts contain related objects, the separation into districts can be highlighted in the visualization. Getting closer brings lower order paths and smaller containers into view. Buildings and small-scale areas can be recognized. Finally, single buildings, small-area landmarks, architectural properties of single buildings, and specialized buildings, like subway stops, can be discerned. 3.2.1. Containers •
A building is a container for information or infrastructure in the Information City. Buildings have a unique address and show their accessibility using doors.
•
Landmarks are special non-access or public access buildings. In the first case, the building has only landmark function, e.g. a clear vista at the end of a path. This case is useful if landmarks are placed at the center of a cluster of related documents if there is no object available in that location to serve as landmark. In a graphical realization of the Information City landmarks can be seen from far away. Major landmarks should be higher than most buildings to provide orienteering aids for users flying over the city.
•
Rooms are containers inside buildings. Their walls may contain doors or windows to access other rooms or the outside. Rooms show their accessibility through doors. Like other containers, they can contain a non-spatial metaphor, like a view-screen. 3.2.2. Navigation Infrastructure •
Paths connect two locations in the city. Therefore, they have starting and ending points that should coincide with landmarks. As in the real city, a path is a continuous element of the Information City. Paths outside buildings are visualized as streets or roads.
•
Intersections of paths are squares. Large squares are major elements in the city. They contain stops of public transport systems and they can contain landmarks. Squares correspond to the nodes in Lynch's city elements.
•
Lines are linear elements that don't adhere to the Euclidean space concept. Transportation, for instance the subway, travels on lines. Lines are connected to the city environment in a few distinct locations. Paths and lines should be visualized differently. Inside buildings (containers) similar elements occur as described above, however, they have different names and sometimes, slightly different functionality. They are the hallway, the lobby and the elevator. The elevator behaves like a line and also provides access to navigational infrastructure outside the building. 3.2.3. Connections and Separations Connections and separations are conceptually similar structures, however separations provide access control. Normal navigation structures do not restrict movement in any way.
•
Doors connect locations inside a building to indoor locations or to the outside. This state of doors (open, closed, locked, ...) shows the accessibility of the corresponding room. Open doors can be looked into. This “preview” shows if the door leads to a room or to an envelope.
•
Windows are similar to doors, but are mostly located in facades. Although they can be used as departure points and destinations for flying, they are not meant as major paths but to look through. A special type of window is the magic window. Windows are a sort of shortcut to rooms inside a building.
3.3. Navigation Tools We distinguish between transportation and navigation tools. Although both of these are navigation in the traditional sense, we consider transportation to be a more passive form of navigation where the user is moved, whereas navigation is an active process. For example, consider the difference between taking a taxi and driving a car. In a taxi, the user instructs the driever as to the desired destination, and then sits back for the ride. On the other hand, driving her own car, the user has to choose the route and steer the vehicle herself. There are several types of navigation and transport metaphors according to the navigation task. Navigation •
Walking is navigation for short distances. It uses paths, squares and all open access structures. Walking can be half-automatic when an address (a link) close by is selected or the user decides to follow a “red carpet”.
•
Driving is a metaphor for fast walking and for covering medium distances.
• Flying is used for long distance navigation. Transportation •
Taxis are like cars, but are not constantly controlled by the user. They can be summoned rom anywhere and are able to navigate using incomplete information. They can even provide a guided tour.
•
The subway provides long-distance transport in the city. It has a set of predefined stops which always coincide with major landmarks. Leaving the subway at those landmarks either places the user in the main lobby or in front of the landmark. The travel time gives a rough indication of the distance traveled. Subways do not show the environment traveled. Subways can be left only at predefined stops but a temporary subway stop can be summoned anywhere outside buildings to enter the subway. Inside buildings elevators provide a connection to the subway. The use of the elevator heightens the user's awareness that she is leaving the building. The subway tunnels through the city space. It connects distant points without traveling through all locations in-between and thus, travels in a different space than a walking user. The subway’s space concept is based on connectedness. This movement of subways in a somewhat detached space was observed already by Kevin Lynch in [29].
Depending on the distance traveled, users apply different navigation and transportation tools, which need to be realized differently. A classification according to distance decides on the visual representation of the navigational activity and its enactment [5, 27] (representation of the navigation process itself). Correct enactment helps users to better understand from where to where they are navigating. The enactment must provide the necessary feedback so that the user does not get disoriented in the navigation process. 3.4. Information Providers Information providers are the information-carrying entities of the city. Some of them are specialized structural elements. Walls and Signs •
The facade of a building is not only an wall, but it provides information about the contents of a building. Facades should show read wear to indicate usage use and visual cues to indicate the content of the building.
•
Information walls present information and also show read wear. They can link to other information walls (tramway or red carpet metaphor) or though magic windows embedded in them. These links should also show their usage. Information walls cannot be moved.
• Signs are small information walls which provide no linking. Movable Information Objects •
Removable information objects are based on source domains like writing pads, books, or business cards, and contain information that is not strictly associated to a location. They may be available as single objects or they may be provided by information dispensers that create an unlimited number of information objects. The dispenser is associated with a fixed location in the city, but the information object itself is movable. Examples of metaphors for dispensers include a newspaper vending machine or an information kiosk.
3.5. Magic Features The city metaphor is usable without magic features, but we believe that it scales well only when magic features are added. In this section, we describe a structuring and a navigation feature. Most navigation and transportation tools (see Section 3.3.) show magic properties but are grouped with the other navigation and transportation tools. •
Envelopes are special rooms. They are outside of the Euclidean space concept of the city. Like rooms, they are accessed through doors, but they give access to very different structures or even another Information City. A city contained in an envelope can be used to represent archived data. The contents of an envelope may actually be larger than the envelope seen from the outside. A transition to an envelope has to be clearly enacted as a magic feature.
Leaving the envelope transfers the user back in front of the door leading to the envelope. Such a transition has to reestablish context for the user e.g. by placing the user high above the city and zooming into the location she occupied before entering the envelope. •
Magic windows (or teleporters) provide a direct connection to other parts of the building, another location in the city, or a view-only connection of another location. They are a special case of the information wall. Magic doors and windows have to clearly show that they are magic features and, as something “special”, they should be used only sparingly.
4. Implementation Issues Even with the elements defined in Section 3 it is not too clear how to start building an Information City. It is unlikely that a complete city can be created in one step. Instead, it has to grow out of the interaction of its users with the city environment. We envision that districts evolve from a basic minimal infrastructure which should be available in every container (building, room,...) consisting of at least one landmark associated with the container. Thus, all containers start as a seeding kernel and expand over time. Large districts are surrounded by a stretch of undefined space (called the void) that allows them to grow and shrink as needed. An alternative to this scheme is to provide a well-developed organization of a district from the very start and adapt it over time. Once an area gets overly developed, it can be transformed to an envelope to create more space in a certain location. The City as a Text-Based Environment The Information City is a conceptual metaphor and it is unlikely we will ever see a complete implementation of all ideas and structures described so far. However information systems are likely to adapt parts of the city for the user interface to large information spaces. This can be done either using a textual virtual environment or in a full-fledged graphical system. In this Section, we describe a few of the advantages of textual environments for realizing the city metaphor. These observations stem from our experience with the Juggler system that used parts of the Information City metaphor (for details see [15, 16]). Textual virtual environments, sometimes called MOOs (Multi User Dungeon Object Oriented) are multi-participant virtual environments in which locations, objects, users and even activities are described by text only [7, 10, 11, 17]. Textual virtual environments can be used to experiment with spatial metaphors as was described in [14, 15]. The text-only representation allows us to realize parts of the metaphor that are difficult to realize graphically. Although metaphors are independent of their representation, most users will find a textual representation more difficult to get used to than a well-designed graphical representation. Textual virtual environments show their strengths mainly in two ways: the representation of read wear, and the enactment of magic features.
Magic Features and Read Wear The enactment of most movements in a MOO is very simple; the description of the room the user arrives in is displayed, and observers see a line describing that a user arrived through the south door, for example. An exit leading to an adjacent room and an exit leading to a distant location are thus indistinguishable, unless the second exit is described as something special, and unless the transition is enacted differently. Believable magic features and special exits in a MOO often feature very distinct descriptions from normal exits. Typically, these descriptions differ in how the exit is described beforehand, and how the process of using the exit is described both to the user and to bystanders [14, 15, 37]. Elaborate textual descriptions of navigational enactment can more easily convey a magic feature. A graphical representation of the process would have to be much more complicated to be credible. On the downside, this textual type of feedback does not easily provide ongoing feedback because the system cannot rely on the reading speed of the user. Also, for features like the Information City's subway system, a textual enactment might be difficult to realize. Similarly, the concept of read wear is difficult to realize well graphically because slight color and size changes over time may well go undetected. In addition it is not clear how to represent aging of information using color. Making a document appear more yellowish over time may actually heighten its visual prominence and therefore, achieve the opposite of the desired effect [36]. A textual description, however, can describe read wear easily as was demonstrated in [15]. As these examples show, there are advantages in using a text-based system for implementing (parts of) the Information City. Magic features and read wear are especially difficult to realize convincingly in a graphical version. A textual representation provides an easy to realize and easy to use alternative. However, for a mass-market implementation of the Information City, text-only implementations will probably not be successful.
5. Conclusions We described a conceptual spatial metaphor, called the Information City. This metaphor is based on knowledge from the field of city-planning, and designed to support navigation in the resulting, easy to learn, virtual city environment. Contrary to other city metaphors in the literature, we define a detailed ontology of city elements, describing how each element pertains to the navigational structure and influences the use of navigation tools. The city is supposed to scale up relatively well because we define magic features that provide short-cuts through the city space. We also define a structural magic feature, called an envelope, that can contain a space that is larger than itself. The envelope and the void, stretches of undefined space, allow the city to expand and shrink without becoming unrecognizable, and therefore, hard to navigate. We also give suggestions on how to initially set up a city.
The Information City is designed to be a multi-user environment. It is not a sterile information graveyard but a social space. The information rich environment of the Information City supports users in giving directions, in recognizing landmarks and so forth. We address several problems implementors will have to face when actually implementing an Information City, among them, how to create the actual structure of the city and how to realize magic features and read wear. One solution we propose is using seeding kernels as basic elements that evolve into larger city structures. Based on our experiences with the Juggler system we propose realizing magic features and read wear textually. However, for a mass-market realization of the city, this solution may not be ideal. With the rate at which technology is progressing, a fully graphical implementation of the Information City is probably possible today, but without a well designed implementation of magic features and read wear, an Information City will fall short of its potential.
Acknowledgments The groundwork for this publication was laid in the first author's Ph.D. thesis, advised by Peter Fleissner and Andrew Frank of the Vienna University of Technology. Work on the Juggler system has been funded in part by a research grant from the Austrian "Fonds zur Förderung der wissenschaftlichen Forschung" (Dr. Erwin Schrödinger Stipendium), Grant J01021-MAT. We want to thank Andrew Frank in particular for his comments and help with the draft of this paper, and our anonymous reviewers for pointing out related work of which we were previously unaware. We would also like to thank Linda Erhard for very detailed proofreading of the paper.
References 1.
Alexander, C. A City is Not a Tree, in Kaplan, S. and Kaplan, R. (Eds.). Humanscape - Environments for People. Ulrich's Books Inc., Ann Arbor, 1982, pp. 377-402.
2.
Andrews, K. Visualizing Cyberspace: Information Visualization in the Harmony Internet Browser, InfoVis'95, IEEE Press, Atlanta, 1995, pp. 97-104.
3.
Andrews, K., Pichler, M., and Wolf, P. Towards Rich Information Landscapes for Visualising Structured Web Spaces, Proc. of 2nd IEEE Symposium on Information Visualization (InfoVis'96), San Francisco, CA, 1996, pp. 62-63.
4.
Barreau, D. and Nardi, B.A. Finding and Reminding - File Organization from the Desktop, SigCHI Bulletin, 27, 3, (1995), pp. 39-43.
5.
Bernstein, M. Enactment in Information Farming, Hypertext'93, Seattle, 1993, pp. 242-249.
6.
Bolter, J.D. Writing Space, Lawrence Erlbaum Associates, 1991.
7.
Bruckman, A. and Resnick, M. Virtual Professional Community: Results from the MediaMOO Project, Convergence, 1, 1, (1995).
8.
Card, S.K., Robertson, G.G., and Mackinley, J.D. The Information Visualizer: An Information Workspace, CHI'91, 1991, pp. 181-188.
9.
Chalmers, M. Using a Landscape Metaphor to Represent a Corpus of Documents, COSIT'93, Springer, Elba, 1993, pp. 377-390.
10. Curtis, P. Mudding: Social Phenomena in Text-Based Virtual Realities, accessible at ftp://parcftp.xerox.com/pub/MOO/papers/DIAC92.ps, 1992. 11. Curtis, P. and Nichols, D.A. MUDs Grow Up: Social Virtual Reality in the Real World, accessible at ftp://parcftp.xerox.com/pub/MOO/papers/MUDsGrowUp.ps, 1993. 12. Dieberger, A. Navigation in Textual Virtual Environments using a City Metaphor, PhD Thesis, Vienna University of Technology, accessible at http://www.lcc.gatech.edu/faculty/dieberger/Thesis/Thesis.html or ftp://ftp.gatech.edu/pub/lcc/andreas/ADieberger.PhDThesis.sea.Hqx, 1994. 13. Dieberger, A. On Magic Features in (Spatial) Metaphors, SigLink Newsletter, 4, 3, (1995), accessible at http://www.lcc.gatech.edu/faculty/dieberger/magic_features.html, pp. 8-10. 14. Dieberger, A. Providing Spatial Navigation for the World Wide Web, in Frank, A.U. and Kuhn, W. (Eds.). Spatial Information Theory - Proceedings of COSIT'95. LNCS 988, Springer, Semmering, Austria, 1995, pp. 93-106. 15. Dieberger, A. Browsing the WWW by interacting with a textual virtual environment - A framework for experimenting with navigational metaphors, Proc. Hypertext'96, Washington DC, 1996, accessible at http://www.lcc.gatech.edu/faculty/dieberger/HT96.paper.html or http://www.cc.gatech.edu/gvu/reports/ techreports97.html. pp. 170-179. 16. Dieberger, A. Supporting Social Navigation on the World Wide Web, International Journal of Human-Computer Studies, (1997), accessible at http://www.cc.gatech.edu/gvu/reports/techreports97.html, forthcoming. 17. Erickson, T. From Interface to Interplace: The Spatial Environment as a Medium for Interaction, COSIT'93, Elba, 1993, pp. 391-405. 18. Henderson, D.A. and Card, S. Rooms: The Use of Multiple Virtual Workspaces to reduce Space Contention in a Window-Based Graphical User Interface, ACM Transactions on Graphics, 5, 3, (1986), pp. 211-243. 19. Hendley, R.J., et. al. Narcissus: Visualizing Information, InfoVis'95, IEEE Press, Atlanta, 1995, pp. 90-96. 20. Hill, W. and Terveen, L. Using frequency-of-mention in public conversations for social filtering, Proc. of CSCW'96, ACM Press, Boston, MA, 1996, pp. 106-112. 21. Hill, W.C. and Hollan, J.D. Edit Wear and Read Wear, CHI'92, ACM Press, Monterey, 1992, pp. 3-9.
22. Ingram, R. and Benford, S. Legibility Enhancement for Information Visualization, Proc. IEEE Visualization'95, Atlanta, GA, 1995, accessible at ftp://ftp.crg.cs.nott.ac.uk/pub/papers/VIZ95.ps.gz. 23. Ingram, R., Bowers, J., and Benford, S. Building Virtual Cities: Applying Urban Planning Principles to the Design of Virtual Environments, Proc. VRST'96, ACM Press, HongKong, 1996, accessible at ftp://ftp.crg.cs.nott.ac.uk/pub/papers/VRST96.ps.gz. 24. Jones, W. and Dumais, S. The Spatial Metaphor for User Interfaces: Experimental Tests of Reference by Location versus Name, ACM Transactions on Office Information Systems, 4, 1, (1986), pp. 42-63. 25. Kuhn, W. and Blumenthal, B. Spatialization: Spatial Metaphors for User InterfacesCHI'96 Course Notes, 1996. 26. Kuipers, B. Modeling Spatial Knowledge, Cognitive Science, 2, (1978), pp. 129153. 27. Laurel, B. Computers as Theatre, Addison-Wesley, 1991. 28. Lynch, K. Good City Form, MIT Press, 1981. 29. Lynch, K. The Image of the City, MIT Press, 1982. 30. Malone, T. How Do people Organize Their Desks? Implications for the Design of Office Information Systems, ACM Transactions on Office Information Systems, 1, 1, (1983), pp. 99-112. 31. Maltz, D. and Ehrlich, K. Pointing The Way: Active Collaborative Filtering, CHI'95, ACM Press, Denver, CO, 1995, pp. 202-209. 32. Mukherjea, S. and Foley, J.D. Visualizing the World-Wide Web with the Navigational View Builder, GVU report, GVU-TR 95-09, 1995, accessible at ftp://ftp.gvu.gatech.edu/pub/gvu/tech-reports/95-09.ps.Z. 33. Nielsen, J. Multimedia and Hypertext - The Internet and Beyond, Academic Press, Cambridge, 1995. 34. Poblete, F., Chignell, M.H., and Chaffey, A.V. No Free Ride: When Information Visualization Doesn't Promote Learning of Information Structure, University of Toronto, Dept. of Industrial Engineering report, TR #96-01, 1996. 35. Rose, D.E., Borenstein, J.J., and Tiene, K. MessageWorld: A new Approach to Facilitating Asynchronous Group Communication, CIKM'95 (Conf. on Information & Knowledge Management), Baltimore, MD, 1995, pp. 266-273. 36. Solomon, G. New Use for Color, in Laurel, B. (Ed.) The Art of Human Computer Interface Design. Addison Wesley, 1990, pp. 169-178. 37. Tromp, J.G. and Dieberger, A. MUDs as text-based spatial user interfaces and research tools, Journal of Intelligent Systems, 5, 2-4, (1995), pp. 179-202.
