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A diagram is a two-dimensional geometric symbolic representation of information according to some visualization technique. Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface. The word graph is sometimes used as a synonym for diagram.

[edit] Overview

A diagram is a 2D geometric symbolic representation of information according to some visualization technique. Sometimes, the technique uses a 3D visualization which is then projected onto the 2D surface. The term diagram in common sense can have two meanings.

• visual information device : Like the term "illustration" the diagram is used as a collective term standing for the whole class of technical genres, including graphs, technical drawings and tables.^[1]
• specific kind of visual display : This is only the genre, that show qualitative data with shapes that are connected by lines, arrows, or other visual links.

In science you will find the term used in both ways. For example Anderson (1997) stated more general "diagrams are pictorial, yet abstract, representations of information, and maps, line graphs, bar charts, engineering blueprints, and architects' sketches are all examples of diagrams, whereas photographs and video are not".^[2] On the other hand Lowe (1993) defined diagrams as specifically "abstract graphic portrayals of the subject matter they represent".^[3]

In the specific sence diagrams and charts contrast computer graphics, technical illustrations, infographics, maps, and technical drawings, by show "abstract rather than literal representations of information".^[1] The essences of a diagram can be seen as:^[1]

• a form of visual formatting devices
• a display that do not show quantitative data, but rather relationships and abstract information
• with building blocks such as geometrical shapes connected by lines, arrows, or other visual links.

Or in Hall's (1996) words "diagrams are simplified figures, caricatures in a way, intended to convey essential meaning".^[4] These simplified figures are often based on set of rules. The basic shape according to White (1984) can be characterized in terms of "elegance, clarity, ease, pattern, simplicity, and validity"^[1]. The elegance for a start is determined by wheter of not the diagram is "the simplest and most fitting solution to a problem".^[5]

[edit] Main diagram types

There are at least the following types of diagrams:

• Graph-based diagrams: these take a collection of items and relationships between them, and express them by giving each item a 2D position, while the relationships are expressed as connections between the items or overlaps between the items; examples of such techniques:See
  • tree diagram
  • network diagram
  • cluster diagram
  • flowchart
  • Euler diagram, Venn diagram, existential graph

tree diagram network diagram flowchart Venn diagram existential graph

• Chart-like diagram techniques, which display a relationship between two variables that take either discrete or a continuous ranges of values; examples:
  • histogram, bar chart
  • pie chart
  • function graph
  • scatter plot
  • table-matrix

histogram bar chart pie chart function graph scatter plot

• Other types of diagrams, e.g.
  • Maps (when stylized, e.g. the map of the London underground)
  • exploded view

train diagram metro map exploded view population density map Pioneer plaque

Thousands of diagram techniques exist. Some more examples follow.

[edit] Specific diagram types

[edit] See also

Wikimedia Commons has media related to: diagrams

Look up diagram in Wiktionary, the free dictionary.

• Chart
• Diagramming
• Diagrammatic reasoning
• List of graphical methods
• Mathematical diagram
• Plot (graphics)
• commons:Specific diagram types - gallery of many diagram types.
• commons:Commons:Diagram resources

[edit] References

[edit] Further reading

• Michael Anderson, Peter Cheng, Volker Haarslev (Eds.) (2000). Theory and Application of Diagrams: First International Conference, Diagrams 2000. Edinburgh, Scotland, UK, September 1-3, 2000. Proceedings.