Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> The focus of the presented work is visualization of routes of objects that change their spatial location in time. The challenge is to facilitate investigation of important characteristics of the movement: positions of the objects at any selected moment, directions, speeds and their changes with the time, overall trajectories and those for any specified interval etc. We propose a dynamic map display controlled through a set of interactive devices called time controls to be used as a support to visual exploration of spatial movement. <s> BIB001 </s> Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> A major difficulty in the analysis of disaggregate activity-travel behavior in the past arises from the many interacting dimensions involved (e.g. location, timing, duration and sequencing of trips and activities). Often, the researcher is forced to decompose activity-travel patterns into their component dimensions and focus only on one or two dimensions at a time, or to treat them as a multidimensional whole using multivariate methods to derive generalized activity-travel patterns. This paper describes several GIS-based three-dimensional (3D) geovisualization methods for dealing with the spatial and temporal dimensions of human activity-travel patterns at the same time while avoiding the interpretative complexity of multivariate pattern generalization or recognition methods. These methods are operationalized using interactive 3D GIS techniques and a travel diary data set collected in the Portland (Oregon) metropolitan region. The study demonstrates several advantages in using these methods. First, significance of the temporal dimension and its interaction with the spatial dimension in structuring the daily space-time trajectories of individuals can be clearly revealed. Second, they are effective tools for the exploratory analysis of activity diary data that can lead to more focused analysis in later stages of a study. They can also help the formulation of more realistic computational or behavioral travel models. <s> BIB002 </s> Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> Graphics have been used since ancient times to portray things that are inherently spatiovisual, like maps and building plans. More recently, graphics have been used to portray things that are metaphorically spatiovisual, like graphs and organizational charts. The assumption is that graphics can facilitate comprehension, learning, memory, communication and inference. Assumptions aside, research on static graphics has shown that only carefully designed and appropriate graphics prove to be beneficial for conveying complex systems. Effective graphics conform to the Congruence Principle according to which the content and format of the graphic should correspond to the content and format of the concepts to be conveyed. From this, it follows that animated graphics should be effective in portraying change over time. Yet the research on the efficacy of animated over static graphics is not encouraging. In cases where animated graphics seem superior to static ones, scrutiny reveals lack of equivalence between animated and static graphics in content or procedures; the animated graphics convey more information or involve interactivity. Animations of events may be ineffective because animations violate the second principle of good graphics, the Apprehension Principle, according to which graphics should be accurately perceived and appropriately conceived. Animations are often too complex or too fast to be accurately perceived. Moreover, many continuous events are conceived of as sequences of discrete steps. Judicious use of interactivity may overcome both these disadvantages. Animations may be more effective than comparable static graphics in situations other than conveying complex systems, for example, for real time reorientations in time and space. <s> BIB003 </s> Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> At the end of the sixties Hagerstrand introduced a space-time model which included features such as a Space-TimePath, and a Space-Time-Prism. His model is often seen as the start of the time-geography studies. Throughout the years his model has been applied and improved to understand our movements through space. Problems studied can be found in different fields of geography, and range from those on an individual movement to whole theories to optimize transportation. From a visualization perspective the Space-Time-Cube was the most prominent element in Hagerstrand’s approach. In its basic appearance these images consist of a cube with on its base a representation of geography (along the x- and y-axis), while the cube’s height represents time (z-axis). A typical Space-Time-Cube could contain the space time-paths of for instance individuals or bus routes. However, when the concept was introduced the options to create the graphics were limited to manual methods and the user could only experience the single view created by the draftsperson. An alternative view on the cube would mean to go through a laborious drawing exercise. Today’s software has options to automatically create the cube and its contents from a database. Data acquisition of space-time paths for both individuals and groups is also made easier using GPS. Today, the user’s viewing environment is, by default, interactive and allows one to view the cube from any direction. In this paper an extended interactive and dynamic visualization environment is proposed, and demonstrated, in which the user has full flexibility to view, manipulate and query the data in a Space-Time-Cube. Included are options to move slider planes along each of the axes to for instance select, or highlight a period in time or location in space. Examples will be discussed in which the time axis is manipulated by for instance changing world time for event time (time cartograms). Creativity should not stop here since it has been shown that especially an alternative perspective on the data will sparkle the mind with new ideas. The user should be allowed to for instance let the x- and/or y-axis be represented by other variables of the theme studied. Since the cube is seen as an integral part of a geovisualization environment the option to link other views with other graphic representation does exist. <s> BIB004 </s> Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> Analyzing observations over time and geography is a common task but typically requires multiple, separate tools. The objective of our research has been to develop a method to visualize, and work with, the spatial interconnectedness of information over time and geography within a single, highly interactive 3D view. A novel visualization technique for displaying and tracking events, objects and activities within a combined temporal and geospatial display has been developed. This technique has been implemented as a demonstratable prototype called GeoTime in order to determine potential utility. Initial evaluations have been with military users. However, we believe the concept is applicable to a variety of government and business analysis tasks <s> BIB005 </s> Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> When displaying thousands of aircraft trajectories on a screen, the visualization is spoiled by a tangle of trails. The visual analysis is therefore difficult, especially if a specific class of trajectories in an erroneous dataset has to be studied. We designed FromDaDy, a trajectory visualization tool that tackles the difficulties of exploring the visualization of multiple trails. This multidimensional data exploration is based on scatterplots, brushing, pick and drop, juxtaposed views and rapid visual design. Users can organize the workspace composed of multiple juxtaposed views. They can define the visual configuration of the views by connecting data dimensions from the dataset to Bertin's visual variables. They can then brush trajectories, and with a pick and drop operation they can spread the brushed information across views. They can then repeat these interactions, until they extract a set of relevant data, thus formulating complex queries. Through two real-world scenarios, we show how FromDaDy supports iterative queries and the extraction of trajectories in a dataset that contains up to 5 million data. <s> BIB006 </s> Visual analytics of movement: An overview of methods, tools and procedures <s> Visualizing trajectories <s> In this paper, we present an interactive visual analytics system, Triple Perspective Visual Trajectory Analytics (TripVista), for exploring and analyzing complex traffic trajectory data. The users are equipped with a carefully designed interface to inspect data interactively from three perspectives (spatial, temporal and multi-dimensional views). While most previous works, in both visualization and transportation research, focused on the macro aspects of traffic flows, we develop visualization methods to investigate and analyze microscopic traffic patterns and abnormal behaviors. In the spatial view of our system, traffic trajectories with various presentation styles are directly interactive with user brushing, together with convenient pattern exploration and selection through ring-style sliders. Improved ThemeRiver, embedded with glyphs indicating directional information, and multiple scatterplots with time as horizontal axes illustrate temporal information of the traffic flows. Our system also harnesses the power of parallel coordinates to visualize the multi-dimensional aspects of the traffic trajectory data. The above three view components are linked closely and interactively to provide access to multiple perspectives for users. Experiments show that our system is capable of effectively finding both regular and abnormal traffic flow patterns. <s> BIB007
The most common types of display for the visualization of movements of discrete entities are static and animated maps  BIB001 and interactive STCs BIB002 BIB004 BIB005 with linear symbols representing trajectories. These displays, as well as some basic interaction techniques, are illustrated in Figure 1 . In Figure 1 (a), there is a map with entire trajectories of ships represented by lines drawn with 10% opacity. Small hollow and filled squares mark, respectively, the start and end positions of the trajectories. By pointing the mouse on the map, the user accesses detailed information about the trajectories. The lines are distinctly coloured according to the ship types; other attributes of the trajectories can also be represented by colouring or line thickness. The interactive legend on the right serves as a filter to hide some ship types from the view and focus on the other types (the figures in the legend show the counts of trajectories for each ship type). In Figure 1 (b), map animation by means of an interactive time filter is demonstrated. The user can select a time window of a desired length (e.g. 3 hours in the screenshot) and move this window forwards and backwards in time by dragging the slider. In response, the map shows only the fragments of the trajectories that were made during the current time window. The figures in the interactive legend show the total counts of trajectories for each ship type and how many of them are visible, at least partly, with the current filter condition. In Figure 1 have been hidden). The time interval shown in the cube has been limited to 20.00 on 1 January 2009 to 11.00 on 3 January 2009 (this operation is known as temporal zoom). The position of the movable plane corresponds to 15.00 on 2 January 2009. To make the lines more visible, their thickness has been increased to two pixels and their opacity has been increased to 100%. As can be seen from these examples, displays showing multiple trajectories may suffer from visual clutter and occlusions. The clutter may be reduced by decreasing the opacity of the symbols but the occlusion problem remains. Besides, both displays provide only limited opportunities for representing various characteristics of the movement and their changes over time. The effectiveness of animated displays raises serious doubts. BIB003 The drawback of the STC, besides occlusion, is distortion of both space and time as a result of projection. It is also quite limited with respect to the length of the time interval that can be effectively studied. Movements in three-dimensional (3D) space, such as in the air or under water, are harder to visualize than movements on a surface. Ware et al.  represent a single trajectory of a whale by a 3D ribbon (in a perspective view) with glyphs on its surface showing the direction of the movement. Hurter et al. BIB006 represent multiple trajectories of aircrafts in horizontal or vertical two-dimensional (2D) projections with animated transitions from one projection to another. Common interaction techniques facilitating visual exploration of trajectories and related data include manipulations of the view (zooming, shifting, rotation, changing the visibility and rendering the order of different information layers, changing opacity levels, etc.), manipulations of the data representation (selection of attributes to represent and visual encoding of their values, e.g. by colouring or line thickness), manipulations of the content (selection or filtering of the objects that will be shown) and interactions with display elements (e.g. access to detailed information by mouse pointing, highlighting, selection of objects to explore in other views, etc.). Multiple co-existing displays are visually linked by using consistent visual encodings (e.g. the same colours) and exhibit coordinated behaviours by simultaneous consistent reaction to various user interactions. These are generic techniques used for various types of data, not for movement data only. They have become standard in information visualization and visual analytics; most of the existing software tools include them. In addition to these generic techniques, Guo et al. BIB007 suggest several interaction techniques specifically designed for trajectories, including selection of trajectories with particular shapes by sketching. Bouvier and Oates 20 suggest original interaction techniques for marking moving objects on an animated display and tracing their movements.