While data visualizations are typically abstract, there is a growing body of work around concrete visualizations, which use familiar objects to convey data. Concrete visualizations can complement abstract ones, especially in immersive analytics, but it is unclear how to design smoothly animated transitions between these two kinds of representations. We investigate a design space of abstract and concrete visualizations, where animated transitions are pathways through the design space. The design space is defined with four axes, each corresponding to a different transformation. We consider different ways to design animated transitions by staging and ordering the transformations along these axes. In a controlled experiment conducted in virtual reality with 16 participants, we compared four types of animated transitions and found quantitative and qualitative evidence of the superiority of a specific staging approach over the simultaneous application of all transformations. Our study pre-registration is available at https://osf.io/8mu73.

A visualization notation is a recurring pattern of symbols used to author specifications of visualizations, from data transformation to visual mapping. Programmatic notations use symbols defined by grammars or domain-specific languages (e.g. ggplot2, dplyr, Vega-Lite) or libraries (e.g. Matplotlib, Pandas). Designers and prospective users of grammars and libraries often evaluate visualization notations by inspecting galleries of examples. While such collections demonstrate usage and expressiveness, their construction and evaluation are usually ad hoc, making comparisons of different notations difficult. More rarely, experts analyze notations via usability heuristics, such as the Cognitive Dimensions of Notations framework. These analyses, akin to structured close readings of text, can reveal design deficiencies, but place a burden on the expert to simultaneously consider many facets of often complex systems. To alleviate these issues, we introduce a metrics-based approach to usability evaluation and comparison of notations in which metrics are computed for a gallery of examples across a suite of notations. While applicable to any visualization domain, we explore the utility of our approach via a case study considering statistical graphics that explores 40 visualizations across 9 widely used notations. We facilitate the computation of appropriate metrics and analysis via a new tool called NotaScope. We gathered feedback via interviews with authors or maintainers of prominent charting libraries ( n=6). We find that this approach is a promising way to formalize, externalize, and extend evaluations and comparisons of visualization notations.

It is common to advise against using 3D to visualize abstract data such as networks, however Ware and Mitchell's 2008 study showed that path tracing in a network is less error prone in 3D than in 2D. It is unclear, however, if 3D retains its advantage when the 2D presentation of a network is improved using edge-routing, and when simple interaction techniques for exploring the network are available. We address this with two studies of path tracing under new conditions. The first study was preregistered, involved 34 users, and compared 2D and 3D layouts that the user could rotate and move in virtual reality with a handheld controller. Error rates were lower in 3D than in 2D, despite the use of edge-routing in 2D and the use of mouse-driven interactive highlighting of edges. The second study involved 12 users and investigated data physicalization, comparing 3D layouts in virtual reality versus physical 3D printouts of networks augmented with a Microsoft HoloLens headset. No difference was found in error rate, but users performed a variety of actions with their fingers in the physical condition which can inform new interaction techniques.

In Augmented Reality (AR), users perceive virtual content anchored in the real world. It is used in medicine, education, games, navigation, maintenance, product design, and visualization, in both single-user and multi-user scenarios. Multi-user AR has received limited attention from researchers, even though AR has been in development for more than two decades. We present the state of existing work at the intersection of AR and Computer-Supported Collaborative Work (AR-CSCW), by combining a systematic survey approach with an exploratory, opportunistic literature search. We categorize 65 papers along the dimensions of space, time, role symmetry (whether the roles of users are symmetric), technology symmetry (whether the hardware platforms of users are symmetric), and output and input modalities. We derive design considerations for collaborative AR environments, and identify under-explored research topics. These include the use of heterogeneous hardware considerations and 3D data exploration research areas. This survey is useful for newcomers to the field, readers interested in an overview of CSCW in AR applications, and domain experts seeking up-to-date information.

Previous work has shown that increased effort and use of one’s body can improve memory. When positioning windows inside a virtual reality, does the use of a larger volume, and using one’s legs to move around, improve ability to later find the windows? The results of our experiment indicate there can be a modest benefit for spatial memory and retrieval time, but at the cost of increased time spent initially positioning the windows.

Recent innovations in visual programming and the use of direct manipulation for programming have demonstrated promise, but also raise questions about how far these approaches can be generalized. To clarify these issues, we present a categorization of systems for visual programming, programming-by-example, and similar systems. By examining each category, we elucidate the advantages, limitations, and ways to extend systems in each category. Our work makes it easier for researchers and designers to understand how visual programming languages (VPLs) and similar systems relate to each other, and how to extend them. We also indicate directions for future research.

We present GoTree, a declarative grammar allowing users to instantiate tree visualizations by specifying three aspects: visual elements, layout, and coordinate system. Within the set of all possible tree visualization techniques, we identify a subset of techniques that are both "unit-decomposable" and "axis-decomposable" (terms we define). For tree visualizations within this subset, GoTree gives the user flexible and fine-grained control over the parameters of the techniques, supporting both explicit and implicit tree visualizations. We developed Tree Illustrator, an interactive authoring tool based on GoTree grammar. Tree Illustrator allows users to create a considerable number of tree visualizations, including not only existing techniques but also undiscovered and hybrid visualizations. We demonstrate the expressiveness and generative power of GoTree with a gallery of examples and conduct a qualitative study to validate the usability of Tree Illustrator.

We propose BarcodeTree (BCT), a novel visualization technique for comparing topological structures and node attribute values of multiple trees. BCT can provide an overview of one hundred shallow and stable trees simultaneously, without aggregating individual nodes. Each BCT is shown within a single row using a style similar to a barcode, allowing trees to be stacked vertically with matching nodes aligned horizontally to ease comparison and maintain space efficiency. We design several visual cues and interactive techniques to help users understand the topological structure and compare trees. In an experiment comparing two variants of BCT with icicle plots, the results suggest that BCTs make it easier to visually compare trees by reducing the vertical distance between different trees. We also present two case studies involving a dataset of hundreds of trees to demonstrate BCT's utility.

Comics are an entertaining and familiar medium for presenting compelling stories about data. However, existing visualization authoring tools do not leverage this expressive medium. In this paper, we seek to incorporate elements of comics into the construction of data-driven stories about dynamic networks. We contribute DataToon, a flexible data comic storyboarding tool that blends analysis and presentation with pen and touch interactions. A storyteller can use DataToon rapidly generate visualization panels, annotate them, and position them within a canvas to produce a visually compelling narrative. In a user study, participants quickly learned to use DataToon for producing data comics.

Many status-quo interfaces for tablets with pen + touch input capabilities force users to reach for device-centric UI widgets at fixed locations, rather than sensing and adapting to the user-centric posture. To address this problem, we propose sensing techniques that transition between various nuances of mobile and stationary use via postural awareness. These postural nuances include shifting hand grips, varying screen angle and orientation, planting the palm while writing or sketching, and detecting what direction the hands approach from. To achieve this, our system combines three sensing modalities: 1) raw capacitance touchscreen images, 2) inertial motion, and 3) electric field sensors around the screen bezel for grasp and hand proximity detection. We show how these sensors enable posture-aware pen+touch techniques that adapt interaction and morph user interface elements to suit fine-grained contexts of body-, arm-, hand-, and grip-centric frames of reference.

We instrumented an immersive VR platform with physiological (heart rate and electrodermal activity) sensors to investigate the use of movement data and physiological data to automatically detect changes in affect (emotional state). 12 users were asked to complete four blocks of tasks requiring them to hit moving targets while standing and moving about. One of the four blocks (in counterbalanced order) was designed to be stressful (S), while the other blocks were designed to be calm (C). The motions required of the users were the same in both conditions; only the visual and audio feedback were different across the S and C conditions. Users' self-scored arousal in the S condition was significantly higher. We analyzed the recorded motions by segmenting out 2747 "fast motions", i.e., intervals of time where the sum of the speed of the hands was above a threshold. A simple machine learning algorithm (a decision tree) could learn to classify these fast motions as either calm or stressed, with ≈80% accuracy, using only two features: the maximum speed achieved during the motion, and the heart rate at the moment of maximum speed, where both features were normalized. If only the maximum speed feature is used (i.e., with no physiological data), ≈70% accuracy is achieved.

We investigate using augmented reality to extend the screen of a smartphone beyond its physical limits with a virtual surface that is co-planar with the phone and that follows as the phone is moved. We call this extension a VESAD, or Virtually Extended Screen-Aligned Display. We illustrate and describe several ways that a VESAD could be used to complement the physical screen of a phone, and describe two novel interaction techniques: one where the user performs a quick rotation of the phone to switch the information shown in the VESAD, and another called "slide-and-hang" whereby the user can detach a VESAD and leave it hanging in mid-air, using the phone to establish the initial position and orientation of the virtual window. We also report an experiment that compared three interfaces used for an abstract classification task: the first using only a smartphone, the second using the phone for input but with a VESAD for output, and the third where the user performed input in mid-air on the VESAD (as detected by a Leap Motion). The second user interface was found to be superior in time and selection count (a metric of mistakes committed by users) and was also subjectively preferred over the other two interfaces. This demonstrates the added value of a VESAD for output over a phone's physical screen, and also demonstrates that input on the phone's screen was better than input in mid-air in our experiment.

Visualization of multiple time series often suffers from overplotting, making it difficult to read the values of curves that are hidden by other curves. We present techniques for horizontally displacing the endpoints of line segments in discrete time series data that (1) enable the depiction of subsets of data and (2) reduce occlusion of endpoints. Because endpoints are not displaced vertically, their y values can still be read and compared. Unlike small multiples, our techniques do not move points with the same x or y values far from each other, making some comparison tasks easier. We present three novel techniques: compressed-superposed, compressed-juxtaposed, and shifted layers. One limitation of our techniques is that they work best when there is only a small number of x values being visualized, and additionally, one of them (compressed-superposed) modifies the slopes of curves in a way that makes the slopes incomparable. Our experimental comparison with three status quo techniques (conventional overlaid, vertically-stacked small multiples, and horizontally-stacked small multiples) shows that our proposed techniques are competitive with status quo techniques and in some cases superior.

Movement data collected through GPS or other technologies is increasingly common, but is difficult to visualize due to overplotting and occlusion of movements when displayed on 2D maps. An additional challenge is the extraction of useful higher-level information (such as meetings) derived from the raw movement data. We present a design study of MovementSlicer, a tool for visualizing the places visited, and behaviors of, individual actors, and also the meetings between multiple actors. We first present a taxonomy of visualizations of movement data, and then consider tasks to support when analyzing movement data and especially meetings of multiple actors. We argue that Gantt charts have many advantages for understanding the movements and meetings of small groups of moving entities, and present the design of a Gantt chart that can nest people within locations or locations within people along the vertical axis, and show time along the horizontal axis. The rows of our Gantt chart are sorted by activity level and can be filtered using a weighted adjacency matrix showing meetings between people. Empty time intervals in the Gantt chart can be automatically folded, with smoothly animated transitions, yielding a multi-focal view. Case studies demonstrate the utility of our prototype.

We design and evaluate a multitouch radial menu for large screens with two desirable properties. First, it allows a single gesture to select a command and then continuously control arguments for that command with unbroken kinesthetic tension. Second, arguments are controlled with 1 or 2 fingers for up to 4 degrees of freedom (DoF). For example, the user may select one command for 4 DoF direct manipulation (translation + scaling + rotation), or another command for 3 DoF camera operations (pan + zoom), using the same two-finger pinch gesture, but with different initial orientations of the gesture to disambiguate. We present a taxonomy to classify previous menuing techniques sharing the first property, and discuss how very few techniques have both of these properties. Our work also extends previous work by Banovic et al. in the following ways: our menu supports submenus and a fast default command, and we experimentally evaluate the effect of varying the number of rings in the menu, the symmetry of the menu, and the use of one hand vs. two hands vs. a stylus and hand.

The speed of graph-based segmentation approaches , such as random walker (RW) and graph cut (GC), depends strongly on image size. For high-resolution images, the time required to compute a segmentation based on user input renders interaction tedious. We propose a novel method, using an approximate contour sketched by the user, to reduce the graph before passing it on to a segmentation algorithm such as RW or GC. This enables a significantly faster feedback loop. The user first draws a rough contour of the object to segment. Then, the pixels of the image are partitioned into “layers” (corresponding to different scales) based on their distance from the contour. The thickness of these layers increases with distance to the contour according to a Fibonacci sequence. An initial segmentation result is rapidly obtained after automatically generating foreground and background labels according to a specifically selected layer; all vertices beyond this layer are eliminated, restricting the segmentation to regions near the drawn contour. Further foreground/background labels can then be added by the user to refine the segmentation. All iterations of the graph-based segmentation benefit from a reduced input graph, while maintaining full resolution near the object boundary. A user study with 16 participants was carried out for RW segmentation of a multi-modal dataset of 22 medical images, using either a standard mouse or a stylus pen to draw the contour. Results reveal that our approach significantly reduces the overall segmentation time compared with the status quo approach ( p < 0.01). The study also shows that our approach works well with both input devices. Compared to super-pixel graph reduction, our approach provides full resolution accuracy at similar speed on a high-resolution benchmark image with both RW and GC segmentation methods . However, graph reduction based on super-pixels does not allow interactive correction of clustering errors. Finally, our approach can be combined with super-pixel clustering methods for further graph reduction, resulting in even faster segmentation.

Graph-based segmentation methods such as the random walker (RW) are known to be computationally expensive. For high resolution images, user interaction with the algorithm is significantly affected. This paper introduces a novel seeding approach for graph-based segmentation that reduces computation time. Instead of marking foreground and background pixels, the user roughly marks the object boundary forming separate regions. The image pixels are then grouped into a hierarchy of increasingly large layers based on their distance from these markings. Next, foreground and background seeds are automatically generated according to the hierarchical layers of each region. The highest layers of the hierarchy are ignored leading to a significant graph reduction. Finally, validation experiments based on multiple automatically generated input seeds were carried out on a variety of medical images. Results show a significant gain in time for high resolution images using the new approach.

GPS, RFID, and other technologies have made it increasingly common to track the positions of people and objects over time as they move through two-dimensional spaces. Visualizing such spatio-temporal movement data is challenging because each person or object involves three variables (two spatial variables as a function of the time variable), and simply plotting the data on a 2D geographic map can result in overplotting and occlusion that hides details. This also makes it difficult to understand correlations between space and time. Software such as GeoTime can display such data with a three-dimensional visualization, where the 3rd dimension is used for time. This allows for the disambiguation of spatially overlapping trajectories, and in theory, should make the data clearer. However, previous experimental comparisons of 2D and 3D visualizations have so far found little advantage in 3D visualizations, possibly due to the increased complexity of navigating and understanding a 3D view. We present a new controlled experimental comparison of 2D and 3D visualizations, involving commonly performed tasks that have not been tested before, and find advantages in 3D visualizations for more complex tasks. In particular, we tease out the effects of various basic interactions and find that the 2D view relies significantly on "scrubbing" the timeline, whereas the 3D view relies mainly on 3D camera navigation. Our work helps to improve understanding of 2D and 3D visualizations of spatio-temporal data, particularly with respect to interactivity.

We investigate the selection of curves within a 2D visualization by specifying their angle or slope. Such angular selection has applications in parallel coordinates, time series visualizations, spatio-temporal movement data, etc. Our interaction technique specifies a region of interest in the visualization (with a position and diameter), a direction, and an angular tolerance, all with a single drag. We experimentally compared this angular selection technique with other techniques for selecting curves, and found that angular selection resulted in a higher number of trials that were successful on the first attempt and fewer incorrectly selected curves, and was also subjectively preferred by participants. We then present the design of a popup lens widget, called the VectorLens, that allows for easy angular selection and also allows the user to perform additional filtering operations based on type of curve. Multiple VectorLens widgets can also be instantiated to combine the results of their filtering operations with boolean operators.

Performance and responsiveness of visual analytics sytems for exploratory data analysis of large datasets has been a long standing problem. We propose a method for incrementally computing visualizations in a distributed fashion by combining a modified MapReduce-style algorithm with a compressed columnar data store, resulting in significant improvements in performance and responsiveness for constructing commonly encountered information visualizations, e.g. bar charts, scatterplots, heat maps, cartograms and parallel coordinate plots. We compare our method with one that queries three other readily available database and data warehouse systems — PostgreSQL, Cloudera Impala and the MapReduce-based Apache Hive — in order to build visualizations. We show that our end-to-end approach allows for greater speed and guaranteed end-user responsiveness, even in the face of large, long-running queries.

Scatterplot matrices (SPLOMs), parallel coordinates, and glyphs can all be used to visualize the multiple continuous variables (i.e., dependent variables or measures) in multidimensional multivariate data. However, these techniques are not well suited to visualizing many categorical variables (i.e., independent variables or dimensions). To visualize multiple categorical variables, 'hierarchical axes' that 'stack dimensions' have been used in systems like Polaris and Tableau. However, this approach does not scale well beyond a small number of categorical variables. Emerson et al. [8] extend the matrix paradigm of the SPLOM to simultaneously visualize several categorical and continuous variables, displaying many kinds of charts in the matrix depending on the kinds of variables involved. We propose a variant of their technique, called the Generalized Plot Matrix (GPLOM). The GPLOM restricts Emerson et al.'s technique to only three kinds of charts (scatterplots for pairs of continuous variables, heatmaps for pairs of categorical variables, and barcharts for pairings of categorical and continuous variable), in an effort to make it easier to understand. At the same time, the GPLOM extends Emerson et al.'s work by demonstrating interactive techniques suited to the matrix of charts. We discuss the visual design and interactive features of our GPLOM prototype, including a textual search feature allowing users to quickly locate values or variables by name. We also present a user study that compared performance with Tableau and our GPLOM prototype, that found that GPLOM is significantly faster in certain cases, and not significantly slower in other cases.

Visualization of dynamically changing networks (graphs) is a significant challenge for researchers. Previous work has experimentally compared animation, small multiples, and other techniques, and found trade-offs between these. One potential way to avoid such trade-offs is to combine previous techniques in a hybrid visualization. We present two taxonomies of visualizations of dynamic graphs: one of non-hybrid techniques, and one of hybrid techniques. We also describe a prototype, called DiffAni, that allows a graph to be visualized as a sequence of three kinds of tiles: diff tiles that show difference maps over some time interval, animation tiles that show the evolution of the graph over some time interval, and small multiple tiles that show the graph state at an individual time slice. This sequence of tiles is ordered by time and covers all time slices in the data. An experimental evaluation of DiffAni shows that our hybrid approach has advantages over non-hybrid techniques in certain cases.

We present an experimental comparison of 4 techniques for smoothly animating changes in a radial tree visualization. Two traditional techniques, linear and staged animation, are compared with two novel techniques a hierarchical animation that proceeds level-by-level through the tree, and a hybrid animation technique that mixes the staged and hierarchical approaches. Users were asked to track changes in nodes of the tree during animated transitions. Results show a significant advantage for the hierarchical and hybrid animation techniques for tracking certain kinds of changes. We then propose guidelines for designing animated transitions. Finally, we present a new popup widget for interactively controlling the progression of an animation that combines advantages of previous widgets.

Abstract One of the fundamental tasks for analytic activity is retrieving (i.e., reading) the value of a particular quantity in an information visualization. However, few previous studies have compared user performance in such value retrieval tasks for different visualizations. We present an experimental comparison of user performance (time and error distance) across four multivariate data visualizations. Three variants of scatterplot (SCP) visualizations, namely SCPs with common vertical axes (SCP‐common), SCPs with a staircase layout (SCP‐staircase), and SCPs with rotated axes between neighboring cells (SCP‐rotated), and a baseline parallel coordinate plots (PCP) were compared. Results show that the baseline PCP is better than SCP‐rotated and SCP‐staircase under all conditions, while the difference between SCP‐common and PCP depends on the dimensionality and density of the dataset. PCP shows advantages over SCP‐common when the dimensionality and density of the dataset are low, but SCP‐common eventually outperforms PCP as data dimensionality and density increase. The results suggest guidelines for the use of SCPs and PCPs that can benefit future researchers and practitioners.

Abstract We present a hybrid visualization technique for compound graphs (i.e. networks with a hierarchical clustering defined on the nodes) that combines the use of adjacency matrices, node‐link and arc diagrams to show the graph, and also combines the use of nested inclusion and icicle diagrams to show the hierarchical clustering. The graph visualized with our technique may have edges that are weighted and/or directed. We first explore the design space of visualizations of compound graphs and present a taxonomy of hybrid visualization techniques. We then present our prototype, which allows clusters (i.e. subtrees) of nodes to be grouped into matrices or split apart using a radial menu. We also demonstrate how our prototype can be used in the software engineering domain, and compare it to the commercial matrix‐based visualization tool Lattix using a qualitative user study.

Abstract Multidimensional multivariate data can be visualized using many different well‐known charts, such as bar charts, stacked bar charts, grouped bar charts, scatterplots, or pivot tables, or also using more advanced high‐dimensional techniques such as scatterplot matrices (SPLOMs) or parallel coordinate plots (PCPs). These many techniques have different advantages, and users may wish to use several charts or data graphics to understand a dataset from different perspectives. We present ConnectedCharts, a technique for displaying relationships between multiple charts. ConnectedCharts allow for hybrid combinations of bar charts, scatterplots, and parallel coordinates, with curves drawn to show the conceptual links between charts. The charts can be thought of as coordinated views, where linking is achieved not only through interactive brushing, but also with explicitly drawn curves that connect corresponding data tuples or axes. We present a formal description of a design space of many simple charts, and also identify different kinds of connections that can be displayed between related charts. Our prototype implementation demonstrates how the connections between multiple charts can make relationships clearer and can serve to document the history of a user's analytical process, leading to potential applications in visual analytics and dashboard design.

We present a prototype interface for visualizing and interacting with univariate time-dependent digital signals, i.e., the kind of signals that might be measured using an oscilloscope and then analyzed to find anomalies in edge timing, overshoot, or other measured characteristics. Our prototype visualizes the data using a standard eye diagram that wraps the signal in time, as well as a parallel coordinates view, and a novel 2.5D layer-based technique based on a drawer metaphor for spreading the eye diagram apart and de-occluding the traces within it. Once a “drawer” is opened, the traces within it can be sorted or grouped according to various attributes, and drilling-down into data can be achieved by opening sub-drawers. We also present a novel technique for browsing eye diagrams called temporal brushing. Initial user feedback from students in electrical engineering is reported. A video demonstrating our prototype can be downloaded at http://profs.logti.etsmtl.ca/mmcguffin/

A standard approach for visualizing multivariate networks is to use one or more multidimensional views (for example, scatterplots) for selecting nodes by various metrics, possibly coordinated with a node-link view of the network. In this paper, we present three novel approaches for achieving a tighter integration of these views through hybrid techniques for multidimensional visualization, graph selection and layout. First, we present the FlowVizMenu, a radial menu containing a scatterplot that can be popped up transiently and manipulated with rapid, fluid gestures to select and modify the axes of its scatterplot. Second, the FlowVizMenu can be used to steer an attribute-driven layout of the network, causing certain nodes of a node-link diagram to move toward their corresponding positions in a scatterplot while others can be positioned manually or by force-directed layout. Third, we describe a novel hybrid approach that combines a scatterplot matrix (SPLOM) and parallel coordinates called the Parallel Scatterplot Matrix (P-SPLOM), which can be used to visualize and select features within the network. We also describe a novel arrangement of scatterplots called the Scatterplot Staircase (SPLOS) that requires less space than a traditional scatterplot matrix. Initial user feedback is reported.

SUMMARY: NAViGaTOR is a powerful graphing application for the 2D and 3D visualization of biological networks. NAViGaTOR includes a rich suite of visual mark-up tools for manual and automated annotation, fast and scalable layout algorithms and OpenGL hardware acceleration to facilitate the visualization of large graphs. Publication-quality images can be rendered through SVG graphics export. NAViGaTOR supports community-developed data formats (PSI-XML, BioPax and GML), is platform-independent and is extensible through a plug-in architecture. AVAILABILITY: NAViGaTOR is freely available to the research community from http://ophid.utoronto.ca/navigator/. Installers and documentation are provided for 32- and 64-bit Windows, Mac, Linux and Unix. CONTACT: [email protected] SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

We present a novel and extensible set of interaction techniques for manipulating visualizations of networks by selecting subgraphs and then applying various commands to modify their layout or graphical properties. Our techniques integrate traditional rectangle and lasso selection, and also support selecting a node's neighbourhood by dragging out its radius (in edges) using a novel kind of radial menu. Commands for translation, rotation, scaling, or modifying graphical properties (such as opacity) and layout patterns can be performed by using a hotbox (a transiently popped-up, semi-transparent set of widgets) that has been extended in novel ways to integrate specification of commands with 1D or 2D arguments. Our techniques require only one mouse button and one keyboard key, and are designed for fast, gestural, in-place interaction. We present the design and integration of these interaction techniques, and illustrate their use in interactive graph visualization. Our techniques are implemented in NAViGaTOR, a software package for visualizing and analyzing biological networks. An initial usability study is also reported.

The need to visualize large social networks is growing as hardware capabilities make analyzing large networks feasible and many new data sets become available. Unfortunately, the visualizations in existing systems do not satisfactorily resolve the basic dilemma of being readable both for the global structure of the network and also for detailed analysis of local communities. To address this problem, we present NodeTrix, a hybrid representation for networks that combines the advantages of two traditional representations: node-link diagrams are used to show the global structure of a network, while arbitrary portions of the network can be shown as adjacency matrices to better support the analysis of communities. A key contribution is a set of interaction techniques. These allow analysts to create a NodeTrix visualization by dragging selections to and from node-link and matrix forms, and to flexibly manipulate the NodeTrix representation to explore the dataset and create meaningful summary visualizations of their findings. Finally, we present a case study applying NodeTrix to the analysis of the InfoVis 2004 coauthorship dataset to illustrate the capabilities of NodeTrix as both an exploration tool and an effective means of communicating results.

Recently, there has been renewed interest in techniques for facilitating the selection of user interface widgets or other on-screen targets with a pointing device. We report research into using target expansion for facilitating selection. Widgets that expand or grow in response to the user's focus of attention allow for a reduced initial size which can help optimize screen space use and may be easier to select than targets that do not expand. However, selection performance could plausibly suffer from a decreased initial widget size. We describe an experiment in which users select a single, isolated target button that expands just before it is selected. Our results show that users benefit from target expansion even if the target only begins expanding after 90% of the distance to the target has been travelled. Furthermore, our results suggest that, for sufficiently large ID values, users are able to take approximately full advantage of the expanded target size. For interfaces with multiple expanding widgets, however, subtle problems arise due to the collisions or overlap that may occur between adjacent expanding widgets. We give a detailed examination of the issues involved in both untiled and tiled multiple expanding targets and present various design strategies for improving their performance.

Many traditional techniques for "looking inside" volumetric data involve removing portions of the data, for example using various cutting tools, to reveal the interior. This allows the user to see hidden parts of the data, but has the disadvantage of removing potentially important surrounding contextual information. We explore an alternate strategy for browsing that uses deformations, where the user can cut into and open up, spread apart, or peel away parts of the volume in real time, making the interior visible while still retaining surrounding context. We consider various deformation strategies and present a number of interaction techniques based on different metaphors. Our designs pay special attention to the semantic layers that might compose a volume (e.g. the skin, muscle, bone in a scan of a human). Users can apply deformations to only selected layers, or apply a given deformation to a different degree to each layer, making browsing more flexible and facilitating the visualization of relationships between layers. Our interaction techniques are controlled with direct, "in place" manipulation, using pop-up menus and 3D widgets, to avoid the divided attention and awkwardness that would come with panels of traditional widgets. Initial user feedback indicates that our techniques are valuable, especially for showing portions of the data spatially situated in context with surrounding data.

There exist several user interface widgets that dynamically grow in size in response to the user's focus of attention. Some of these, such as icons in toolbars, expand to facilitate their selection - allowing for a reduced initial size in an attempt to optimize screen space use. However, selection performance may be degraded by this decreased initial widget size. We describe an experiment which explores the effects of varying parameters of expansion techniques in a selection task. Our results suggest that Fitts' law can model and predict performance in such tasks. They also indicate that performance is governed by the target's final size, not its initial one. Further, performance is dependent on the target's final size even when the target only begins expanding as late as after 90% of the movement towards the target has already been completed. These results indicate that expanding widgets can be used without sacrificing performance