The term "diagram" in its commonly used sense can have a general or specific meaning:
visual information device : Like the term "illustration", "diagram" is used as a collective term standing for the whole class of technical genres, includinggraphs, technical drawings and tables.
specific kind of visual display : This is the genre that shows qualitative data with shapes that are connected by lines, arrows, or other visual links.
In science the term is used in both ways. For example, Anderson (1997) stated more generally: "diagrams are pictorial, yet abstract, representations of information, andmaps,line graphs,bar charts,engineeringblueprints, andarchitects'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 sense diagrams and charts contrast withcomputer graphics, technical illustrations,infographics, maps, andtechnical drawings, by showing "abstract rather thanliteral representations of information".[4] The essence of a diagram can be seen as:[4]
adisplay that does not showquantitative data (numerical data), but rather relationships and abstract information
withbuilding blocks such as geometrical shapes connected bylines,arrows, or other visual links.
Or in Hall's (1996) words "diagrams are simplified figures, caricatures in a way, intended to convey essential meaning".[5] These simplified figures are often based on a set of rules. The basic shape according to White (1984) can be characterized in terms of "elegance, clarity, ease, pattern, simplicity, and validity".[4] Elegance is basically determined by whether or not the diagram is "the simplest and most fitting solution to a problem".[6]
Diagrammatology is the academic study of diagrams. Scholars note that while a diagram may look similar to the thing that it represents, this is not necessary. Rather a diagram may only havestructural similarity to what it represents, an idea often attributed toCharles Sanders Peirce.[7]: 42 Structural similarity can be defined in terms of a mapping between parts of the diagram and parts of what the diagram represents and the properties of this mapping, such as maintaining relations between these parts and facts about these relations. This is related to the concept ofisomorphism, orhomomorphism in mathematics.[7]: 43
Sometimes certaingeometric properties (such as which points are closer) of the diagram can be mapped to properties of the thing that a diagram represents. On the other hand, the representation of an object in a diagram may be overly specific and properties that are true in the diagram may not be true for the object the diagram represents.[7]: 48 A diagram may act as a means of cognitive extension allowingreasoning to take place on the diagram based on which constraints are similar.[7]: 50
Logical or conceptual diagrams, which 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, for example:
^Michael Anderson (1997). "Introduction to Diagrammatic Reasoning", atcs.hartford.edu. Retrieved 21 July 2008.
^Lowe, Richard K. (1993). "Diagrammatic information: techniques for exploring its mental representation and processing".Information Design Journal.7 (1):3–18.doi:10.1075/idj.7.1.01low.
^Bert S. Hall (1996). "The Didactic and the Elegant: Some Thoughts on Scientific and Technological Illustrations in the Middle Ages and Renaissance". in: B. Braigie (ed.)Picturing knowledge: historical and philosophical problems concerning the use of art in science. Toronto: University of Toronto Press. p.9
^abcdPombo, Olga; Gerner, Alexander, eds. (2010).Studies in Diagrammatology and Diagram Praxis. London: College Publications.ISBN978-1-84890-007-3.OCLC648770148.
Bounford, Trevor (2000).Digital diagrams. New York: Watson-Guptill Publications.ISBN978-0-8230-1572-6.
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.
Garcia, M. (ed.), (2012)The Diagrams of Architecture. Wiley. Chichester.
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