[Guest Post by T. Alan Keahey, Ph.D., Visualization Expert in IBM Watson Group]
An interesting question is how the increasing use of mobile devices is likely to affect the design of visualizations in the future. Obviously, the smaller display screens on tablets and smart phones will have a limiting effect on the amount of information that can be displayed. However, the relation between screen size and information content size is not a trivial one, and their impact on proper visualization design runs much more deeply than screen depth. Let me explain.
In terms of pixel count, much progress has been made in display hardware to increase pixel density. In the case of Apple’s iPad, the initial displays had 1024x768 pixels, which works out to about 786K pixels at 132 pixels per inch (PPI). The retina display quadrupled that resolution to 2048x1536 pixels, which gives just over 3 million pixels at 264 PPI. However, 264 PPI is nearing the limits of perceptibility, particularly when taking into account individual variances in visual acuity. As a consequence, many of the additional pixels provided by the high-resolution displays serve a greater purpose to increase the fidelity of existing visual elements rather than to visually encode new ones.
The larger effect of this is that we are at or near a saturation point for the amount of pixels that can be effectively distinguished in a tablet size display, and visualization designers cannot rely on future screen resolution improvements to increase this limit.
Another significant factor in mobile displays involves the touch interfaces. Apple Human Interface guidelines call for a touch point target size of around 44 points, which is equivalent to 0.61” or 15.5mm on each side. If we overlay a grid with those sized squares on a traditional 9.7” diagonal tablet, that gives us a touch grid of only 12x9 or 108 points. With some careful design, we can increase this number somewhat, perhaps doubling each dimension for a total of 400 touch points on a tablet device.
These two factors of asymptotic pixel density and limited interactivity resolution are going to place a premium on the effective use of screen real estate going forward. This, in turn, will lead towards a de-cluttering of the visual interface, eliminating many of the “chart junk” and other nonessential elements. I see two key areas where this is likely to have a deeper impact in visualization design going forward:
1) Increased re-purposing of the visualization metaphor as a tool, not just for showing the information, but also as the principal navigation mechanism for exploring that same information. This approach helps to eliminate the need for external controls (buttons, menus, etc.) and, if done correctly, allows for a fluid and intuitive means of information navigation.
2) Placing a higher priority on showing only the most focused and relevant information, but in a way that still allows the viewer to flexibly explore the entire space of information in pursuit of the golden nuggets. In contrast to more traditional visualization systems that still rely on the user manually slicing and dicing their way through the entire dataset, this new priority will drive systems towards the use of increasingly sophisticated integrated analytics that assist the viewer in finding the most interesting features and patterns in the data.
This example above from Watson Analytics shows how relatively well known visual metaphors (such as this treemap) can be used on a mobile device, integrated with powerful cognitive analytics, including using simple gestures and natural language processing to facilitate interactions.
Stronger requirements for guiding the viewer to the more relevant information are not unique to visualization capabilities. We see similar needs being driven by the increasingly large scales of Big Data. In order to match the scales of Big Data with the capacities of display systems and the human visual system we will need to rely on more sophisticated analytics that are closely tied to the visualization-query sense-making process. Taken together, these drivers or larger data on smaller displays are sure to have a profound impact on the sophistication of the next generation of visualization systems.
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Dr. T. Alan Keahey has played a leading role in the research and development of highly innovative information visualization systems for close to 20 years. His experience spans a wide range of environments including national labs research scientist, research director at a Lucent Bell Labs spin off, and founder of his own visualization R&D company. He thrives on anchoring connections between the capabilities created in research environments and the real-world needs of business customers. Alan is currently a visualization expert in the IBM Watson Group, where he works to drive the innovative and effect use of visualization across IBM and their customers. He blogs about visualization and related topics at HolisticSofa.com.