Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> Big information worlds cause big problems for interfaces. There is too much to see. They are hard to navigate. An armada of techniques has been proposed to present the many scales of information needed. Space-scale diagrams provide an analytic framework for much of this work. By representing both a spatial world and its different magnifications explicitly, the diagrams allow the direct visualization and analysis of important scale related issues for interfaces. <s> BIB001 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> Fitts pointing model has proven extremely useful forunderstanding basic selection in WIMP user interfaces. Yet todaysinterfaces involve more complex navigation within electronicenvironments. As navigation amounts to a form of multi-scalepointing, Fitts model can be applied to these more complex tasks.We report the results of a preliminary pointing experiment thatshows that users can handle higher levels of task difficulty withtwo-scale rather than traditional one-scale pointing control. Also,in tasks with very high-precision hand movements, performance ishigher with a stylus than with a mouse. <s> BIB002 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> Our ability to accumulate large, complex (multivariate) data sets has far exceeded our ability to effectively process them in searching for patterns, anomalies and other interesting features. Conventional multivariate visualization techniques generally do not scale well with respect to the size of the data set. The focus of this paper is on the interactive visualization of large multivariate data sets based on a number of novel extensions to the parallel coordinates display technique. We develop a multi-resolution view of the data via hierarchical clustering, and use a variation of parallel coordinates to convey aggregation information for the resulting clusters. Users can then navigate the resulting structure until the desired focus region and level of detail is reached, using our suite of navigational and filtering tools. We describe the design and implementation of our hierarchical parallel coordinates system which is based on extending the XmdvTool system. Lastly, we show examples of the tools and techniques applied to large (hundreds of thousands of records) multivariate data sets. <s> BIB003 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> We propose a navigation technique for browsing large documents that integrates rate-based scrolling with automatic zooming. The view automatically zooms out when the user scrolls rapidly so that the perceptual scrolling speed in screen space remains constant. As a result, the user can efficiently and smoothly navigate through a large document without becoming disoriented by extremely fast visual flow. By incorporating semantic zooming techniques, the user can smoothly access a global overview of the document during rate-based scrolling. We implemented several prototype systems, including a web browser, map viewer, image browser, and dictionary viewer. An informal usability study suggests that for a document browsing task, most subjects prefer automatic zooming and the technique exhibits approximately equal performance time to scroll bars , suggesting that automatic zooming is a helpful alternative to traditional scrolling when the zoomed out view provides appropriate visual cues. <s> BIB004 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> Large 2D information spaces, such as maps, images, or abstract visualizations, require views at various level of detail: close ups to inspect details, overviews to maintain (literally) an overview. Users often switch between these views. We discuss how smooth animations from one view to another can be defined. To this end, a metric on the effect of simultaneous zooming and panning is defined, based on an estimate of the perceived velocity. Optimal is defined as smooth and efficient. Given the metric, these terms can be translated into a computational model, which is used to calculate an analytic solution for optimal animations. The model has two free parameters: animation speed and zoom/pan trade off. A user experiment to find good values for these is described. <s> BIB005 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> Since the advent of graphical user interfaces, electronic information has grown exponentially, whereas the size of screen displays has stayed almost the same. Multiscale interfaces were designed to address this mismatch, allowing users to adjust the scale at which they interact with information objects. The technology has progressed quickly and the theory has lagged behind. Multiscale interfaces pose a stimulating theoretical challenge: reformulating the classic target-acquisition problem from the physical world into an infinitely rescalable electronic world. We address this challenge by extending Fitts' original pointing paradigm: we introduce the scale variable, thus defining a multiscale pointing paradigm. This article reports on our theoretical and empirical results. We show that target-acquisition performance in a zooming interface must obey Fitts' law and, more specifically, that target-acquisition time must be proportional to the index of difficulty. Moreover, we complement Fitts' law by accounting for the effect of view size on pointing performance, showing that performance bandwidth is proportional to view size, up to a ceiling effect. Our first empirical study shows that Fitts' law does apply to a zoomable interface for indices of difficulty up to and beyond 30 bits. whereas classical Fitts' law studies have been confined in the 2-10 bit range. Our second study demonstrates a strong interaction between view size and task difficulty for multiscale pointing, and shows a surprisingly low ceiling. We conclude with implications of these findings for the design of multiscale user interfaces. <s> BIB006 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> High precision parameter manipulation tasks typically require adjustment of the scale of manipulation in addition to the parameter itself. This paper introduces the notion of Zoom Sliding, or Zliding, for fluid integrated manipulation of scale (zooming) via pressure input while parameter manipulation within that scale is achieved via x-y cursor movement (sliding). We also present the Zlider (Figure 1), a widget that instantiates the Zliding concept. We experimentally evaluate three different input techniques for use with the Zlider in conjunction with a stylus for x-y cursor positioning, in a high accuracy zoom and select task. Our results marginally favor the stylus with integrated isometric pressure sensing tip over bimanual techniques which separate zooming and sliding controls over the two hands. We discuss the implications of our results and present further designs that make use of Zliding. <s> BIB007 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> This article introduces the OrthoZoom Scroller, a novel interaction technique that improves target acquisition in very large one-dimensional spaces. The OrthoZoom Scroller requires only a mouse to perform panning and zooming in a 1D space. Panning is performed along the slider dimension while zooming is performed along the orthogonal one. We present a controlled experiment showing that the OrthoZoom Scroller is about twice as fast as Speed Dependant Automatic Zooming to perform pointing tasks whose index of difficulty is in the 10-30 bits range. We also present an application to browse large textual documents with the OrthoZoom Scroller that uses semantic zooming and snapping on the structure. <s> BIB008 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Zoom and Pan <s> Treemaps provide an interesting solution for representing hierarchical data. However, most studies have mainly focused on layout algorithms and paid limited attention to the interaction with treemaps. This makes it difficult to explore large data sets and to get access to details, especially to those related to the leaves of the trees. We propose the notion of zoomable treemaps (ZTMs), an hybridization between treemaps and zoomable user interfaces that facilitates the navigation in large hierarchical data sets. By providing a consistent set of interaction techniques, ZTMs make it possible for users to browse through very large data sets (e.g., 700,000 nodes dispatched amongst 13 levels). These techniques use the structure of the displayed data to guide the interaction and provide a way to improve interactive navigation in treemaps. <s> BIB009
Zooming and panning changes the current view of a visualization, respectively, changing the size and position of the viewport window on the visual substrate BIB001 ,  (Fig. 3) . In a way, zoom and pan operations can be seen as spatial filters that control which visual data entities to display on the screen as well as the screen space allocated to each entity. These operations are typically used to take a closer look at parts of a visualization without actually revealing more detail in the data. Navigation in multiscale spaces has recently been a focus in the human-computer interaction community because of its applicability to high-precision selection BIB006 , BIB002 . Many of these interaction techniques-such as speed-dependent automatic zooming (SDAZ) BIB004 , Zliding BIB007 , and OrthoZoom BIB008 -could be used to navigate the multiscale structures defined by the hierarchical aggregated visualizations discussed in this paper. Fua et al. BIB003 describe a specialization of zooming for parallel coordinates that they call dimension zooming where each dimension axis is zoomed independently; this approach can easily be employed for other visualization techniques, such as using different axis scales in scatterplots or trivially for space-filling techniques such as treemaps. On the other hand, it does not make sense for visualizations where spatial location has no intrinsic meaning, such as for node-link diagrams. On a related note, the snap-zoom BIB009 technique is a variant of axis-independent zooming for continuous treemap navigation where the scale factor for the axes depends on a view-dependent (e.g., dynamically changing) layout criterion. This is a good example of how to customize a general interaction technique to the characteristics of a specific visualization while still retaining the same interaction pattern. For the purpose of balancing zoom and pan operations, the work of van Wijk and Nuij BIB005 on smooth and efficient zooming and panning is particularly relevant. They present a computational model that can be used to control the speed and behavior of animated transitions from different viewports on a large visual space. However, this is clearly not relevant when the viewer has direct control over zooming and panning.