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Presenting Visual Information Responsibly

Vol.33 No.3 August 1999
ACM SIGGRAPH


Are Faithfulness and Accuracy Necessary?



Nahum Gershon
Nahum Gershon
The MITRE Corporation



Figure 1a
Figure 1b
Figure 1: Old fruit crate and can labels.


Figure 2
Figure 2: A known visual illusion—the line on the top looks longer than the one in the bottom due to perspective lines.


Figure 3
Figure 3: In the 3D representation, the pie piece in the front looks bigger than it is in reality. The relative size of the slices is better represented in t he 2D rendering.


Figure 4
Figure 4: The width of the highways is deliberately represented out of scale. Otherwise, it will not be visible.


Figure 5
Figure 5: Schematic representation of the anatomy of the Cough Reflex. The depiction of the human body is used only for localization of relevant pieces of information and thus is represented schematically.



“We are approximate beings...Animals don’t require precise measurements and high accuracy to function. Machines do.”
— Don Norman, The Invisible Computer [1]

The notion of perfection exists in the commercial world (see, for example, Figure 1) and sometimes in human expectations. In reality, life is not perfect and never will be. We do not always get the data and information for which we strive with the precision or consistency required by the problem we need to solve. For example, we know the locations of objects in space only up to a certain level of accuracy.

The visualization process, representing given data and information in a visual form, is not a perfect science. The imperfect nature of the visualization process is due to two main factors.

First, the visual representation can be inherently less accurate than numbers or words. For example, a digital watch displays the time down to a fraction of a second, while an analog watch (representing the time visually) does it with lower accuracy. Most people nowadays still prefer an analog watch to a digital one because it is faster to read the analog representation. Also, as Don Norman (1998) noted, “...people are analog, not digital; biological, not mechanical...” [1] Moreover, “We are approximate beings...Animals don’t require precise measurements and high accuracy to function. Machines do.” [1] This does not mean, however, that accuracy and precision are never important. In some situations (e.g., in measuring running time in athletic races, and in finance dealings), we do need enough accuracy of the data and information to understand reality and to be able to reach reasonable and timely decisions.

The second factor affecting how accurately visualization portrays reality is the quality of choice of the visualization parameters. For example, the choice of color can affect what parts of the information will be evident to the user. Inappropriate color scale can mask important pieces of relevant information. Additional examples where the visualization process causes the user to perceive reality falsely are given in Figures 2 and 3.

Knowing what pieces of information or data are accurate, complete, consistent and certain; and which are not, and by how much, can be essential for understanding the data and information and for reaching sound decisions. If we understand these sources of imperfection, we would be better suited to:

  • Inform the user (when necessary) about the quality of the data and information
  • Perform the visualization process without creating visualization artifacts

Sometimes, we deliberately need to portray reality falsely. As nicely expressed by Richard Saul Wurman in Information Anxiety, “Maps aren’t mirrors of reality; they are a means of understanding it. To accomplish this, map makers can reduce, distill, exaggerate or abstract reality. Their mission is to capture the salient aspects of a particular reality that would enable someone to understand it...” [2] In Figure 4, the width of the highways is not represented in scale. If the map maker would have represented the highway width on scale, it would not be visible on the map. Since we know this fact, nobody with a sound mind would try and measure the highway width from this map.

In visualizing known objects, we can revert to schematic diagrams. For example, in Figure 5, the human body depiction does not represent the human body as it appears in reality. It is only used as a framework background for the display of the pertinent information related to different locations in the body. In cases where the image of the data and information is not known a priori, we have a problem. This is important especially when representing abstract data and information and the visualizations are used for exploration.

Thus, whether we need to represent the data and information faithfully will depend upon the task, user and usage.

In conclusion, in spite of the popular belief, faithfulness and accuracy are not always a good idea. There are cases where faithfulness and accuracy are not needed and could even be detrimental. For example, too much data and information on the screen could produce clutter and perplex the user. In such cases, it is advisable to use schematic representations. Making the user fully aware that parts of the visualization are schematic will minimize the occurrence of situations where the schema is taken seriously.

References

  1. Norman, Donald, A. The Invisible Computer, MIT Press, Cambridge, MA, 1998.
  2. Wurman, Richard Saul. Information Anxiety, Bantam Books, NY, 1990.




Nahum Gershon is a Senior Principal Scientist at The MITRE Corp. His work is concerned with information and data visualization, network browsers, image processing, data organization and analysis of medical, environmental and other multidimensional data. He pursues research in the use of understanding of the perceptual system in improving the visualization process.

Gershon has published extensively in the area of visualization and has organized and chaired seven SIGGRAPH panels. He served as a Co-Chair of Visualization ‘94 and ‘95 conferences and co-organized the Information Visualization Symposia (1995-98).

Nahum Gershon
The MITRE Corporation
1820 Dolley Madison Blvd.
McLean, VA 22102

Tel: +1-703-883-7518
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