- a schematic representation of the reality
- a mean from which people construct internal mental representation of the world
We refer with the term graphics to representations where the primary purpose is art or entertainment, while the term information graphics is used for graphics with the purpose of visually present information
Information graphics are useful because:
- may illustrate one or more relationships among entities represented
- may be a shorthand way to present information
- allows to analyse trends, patterns, or comparisons on entities represented
Why we use graphics
(Larkin & Simon, 2001) compared diagrammatic representations with sentential (verbal) representations. They found that diagrammatic representations can be superior to a verbal description for the following proprieties:
- Locality – is enabled by grouping together information that is used together. This avoids large amounts of search and allows different information closely located to be processed simultaneously. For example, the figure below puts together information about the history of two different stock market indexes and allows to process their evolution immediately.
- Minimal labelling– is enabled by using location to group information about a single element, avoiding the need to match symbolic labels and leading to reducing the working memory load. For example, the image below shows driving directions from Lugano to Pisa provided in graphical format; it uses visual entities such as lines depicted in red with a yellow stripe in the middle to denote a highway. Turning points (such as in Parma in the example) are clearly indicated by a crossing of the roads. Symbolic textual representations used in the textual format of the map are unnecessary because the connections are explicitly represented in the graphics.
- Perceptual enhancement– is enabled by supporting a large number of perceptual inferences which are easy for humans to perform. For example, in the figure below the link between deaths from cholera and the location of a water pump responsible for the spread of cholera could be recognised immediately.
According to (Tufte, 83), a good graphics must reflect the followin ideas:
- Consists of complex ideas communicated with clarity, precision and efficiency
- Gives to the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space
- Tells the truth about the data.
Graphical excellence: Tufte’s rules
From (Tufte, 93): Graphical displays should:
- Show the data
- Induce the viewer to think about the substance rather than about the methodology of graphics production
- Avoid distorting what the data says
- Present many numbers in a small space
- Make large data sets coherently
- Encourage inferential processes, such as comparing different pieces of data
- Give different perspectives on the data -from broad overview to the fine structure
- Serve reasonably clear purpose: description, exploration, tabulation, or decoration