diagram

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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 word graph is sometimes used as a synonym for diagram.

Overview

The term diagram

Diagram has two meanings in common sense.^[1]

1. A collective term for any visual information device, like the term "illustration" often used as a representative term, to stand for the whole class of technical genres, including graphs and tables.
2. The specific class of visual display, that show qualitative data with shapes that are connected by lines, arrows, or other visual links.

The term diagram is used in both meanings in science. For example Michael Anderson (1997) stated "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 Richard K. Lowe (1993) defined diagrams as "abstract graphic portrayals of the subject matter they represent", and only include the typical visual forms as area diagrams, flow charts, idea diagrams, and PERT charts.^[3]

The word "diagram" is often coupled together with the word "chart" as in "charts and diagrams", within the larger conceptual framework of qualitative rather than quantitative displays. Charts can contain both quantitative and qualitative information. The term "charts and diagrams" is specially meant to address one class of genre: the kind that communicates qualitative information.^[1]

Characteristics

Diagrams and charts, in contrast to computer graphics, technical illustrations, infographics, maps, and technical drawings, show abstract rather than literal representations of information.^[1] In essence diagrams are:^[1]

• visual formatting devices
• that do not display quantitative data, but rather relationships and abstract information
• represented by shapes that are connected by lines, arrows, or other visual links.

Diagrams are usually simplified figures, caricatures in a way, intended to convey essential meaning.^[3] According to Jan V. White (1984) the characteristics of a good diagram are elegance, clarity, ease, pattern, simplicity, and validity. Elegance for White means that what you are seeing in the diagram is the simplest and most fitting solution to a problem.^[4]

Applications

Diagrams and charts are very good at showing actions, processes, events and ideas. In addition, for a number of visually inclined people, charts and diagrams also provide a visual method of thinking out ideas. They are devices for persons or groups to use in decision-making. For computer programmers, structured diagrams offer precision, fast development, automated checking, key linkages, and above all, standardization.^[5]

Diagrams, according to Lee E. Brasseur (2003), are essentially drawings with text. They consist of basic lines and shapes that convey an idea. The broad category of drawings in a larger sense can include very realistic portrayals of life or objects, but diagrams are a kind of drawing that tend to show a basic abstract structure rather than a more highly contextualized or detailed view. They can be thought of as providing something akin to the essence of a situation or an idea.^[1]

History

The earliest seeds of visualization, according to Michael Friendly (2008), arose in geometric diagrams, in tables of the positions of stars and other celestial bodies, and in the making of maps to aid in navigation and exploration. They origin from prehistoric times, and had their own appearances in every early civilisation. By the 16th century, techniques and instruments for precise observation and measurement of physical quantities were well-developed— the beginnings of the husbandry of visualization. The 17th century saw great new growth in theory and the dawn of practice, such as the rise of analytic geometry, theories of errors of measurement, the birth of probability theory, and the beginnings of demographic statistics and political arithmetic.^[6]

Over the 18th and 19th centuries, numbers pertaining to people, and social, moral, medical, and economic statistics began to be gathered in large and periodic series. Moreover, the usefulness of these bodies of data for planning, for governmental response, and as a subject worth of study in its own right, began to be recognized. This was accompanied by a rise in visual thinking. Diagrams were used to illustrate mathematical proofs and functions, nomograms were developed to aid calculations, various graphic forms were invented to make the properties of empirical numbers. Their trends, tendencies, and distributions were more easily communicated, or accessible to visual inspection. As well, the close relation of the numbers of the state. The origin of the word statistics and its geography gave rise to the visual representation of such data on maps, now called thematic cartography.^[6]

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.

Specific diagram types

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

References

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.