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From Wikipedia, the free encyclopedia

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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.



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 sense 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 whether or not the diagram is "the simplest and most fitting solution to a problem".[5]

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:
  • Chart-like diagram techniques, which display a relationship between two variables that take either discrete or a continuous ranges of values; examples:
  • Other types of diagrams, e.g.,

Thousands of diagram techniques exist. Some more examples follow.

Specific diagram types




List of modeling languages




  • Line of balance







See also


  1. ^ a b c d Brasseur, Lee E. (2003). Visualizing technical information: a cultural critique. Amityville, N.Y: Baywood Pub. ISBN 0-89503-240-6. 
  2. ^ Michael Anderson (1997). "Introduction to Diagrammatic Reasoning". Retrieved 21 July 2008.
  3. ^ Lowe, Richard K. (1993). "Diagrammatic information: techniques for exploring its mental representation and processing". Information Design Journal 7 (1): 3–18. 
  4. ^ 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
  5. ^ White, Jan V. (1984). Using charts and graphs: 1000 ideas for visual persuasion. New York: Bowker. ISBN 0-8352-1894-5. 
  6. ^ HIPO diagram

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.

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

DIAGRAM (Gr. &Lypapua, from SLrypb4av, to mark out by lines, a figure drawn in such a manner that the geometrical relations between the parts of the figure illustrate relations between other objects. They may be classed according to the manner in which they are intended to be used, and also according to the kind of analogy which we recognize between the diagram and the thing represented. The diagrams in mathematical treatises are intended to help the reader to follow the mathematical reasoning. The construction of the figure is defined in words so that even if no figure were drawn the reader could draw one for himself. The diagram is a good one if those features which form the subject of the proposition are clearly represented.

Diagrams are also employed in an entirely different way - namely, for purposes of measurement. The plans and designs drawn by architects and engineers are used to determine the value of certain real magnitudes by measuring certain distances on the diagram. For such purposes it is essential that the drawing be as accurate as possible. We therefore class diagrams as diagrams of illustration, which merely suggest certain relations to the mind of the spectator, and diagrams drawn to scale, from which measurements are intended to be made. There are some diagrams or schemes, however, in which the form of the parts is of no importance, provided their connexions are properly shown. Of this kind are the diagrams of electrical connexions, and those belonging to that department of geometry which treats of the degrees of cyclosis, periphraxy, linkedness and knottedness.

Diagrams purely Graphic and mixed Symbolic and Graphic

Diagrams may also be classed either as purely graphical diagrams, in which no symbols are employed except letters or other marks to distinguish particular points of the diagrams, and mixed diagrams, in which certain magnitudes are represented, not by the magnitudes of parts of the diagram, but by symbols, such as numbers written on the diagram. Thus in a map the height of places above the level of the sea is often indicated by marking the number of feet above the sea at the corresponding places on the map. There is another method in which a line called a contour line is drawn through all the places in the map whose height above the sea is a certain number of feet, and the number of feet is written at some point or points of this line. By the use of a series of contour lines, the height of a great number of places can be indicated on a map by means of a small number of written symbols. Still this method is not a purely graphical method, but a partly symbolical method of expressing the third dimension of objects on a diagram in two dimensions.

In order to express completely by a purely graphical method the relations of magnitudes involving more than two variables, we must use more than one diagram. Thus in the arts of construction we use plans and elevations and sections through different planes, to specify the form of objects having three dimensions. In such systems of diagrams we have to indicate that a point in one diagram corresponds to a point in another diagram. This is generally done by marking the corresponding points in the different diagrams with the same letter. If the diagrams are drawn on the same piece of paper we may indicate corresponding points by drawing a line from one to the other, taking care that this line of correspondence is so drawn that it cannot be mistaken for a real line in either diagram. (See GEOMETRY: Descriptive.) In the stereoscope the two diagrams, by the combined use of which the form of bodies in three dimensions is recognized, are projections of the bodies taken from two points so near each other that, by viewing the two diagrams simultaneously, one with each eye, we identify the corresponding points intuitively. The method in which we simultaneously contemplate two figures, and recognize a correspondence between certain points in the one figure and certain points in the other, is one of the most powerful and fertile methods hitherto known in science. Thus in pure geometry the theories of similar, reciprocal and inverse figures have led to many extensions of the science. It is sometimes spoken of as the method or principle of Duality. (See GEOMETRY Projective.)

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Simple English

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The English Wiktionary has a dictionary definition (meanings of a word) for:

A diagram is a simplified and structured visual representation of concepts, ideas, constructions, relations, statistical data, anatomy etc used in all aspects of human activities to visualize and clarify the topic.


Basic diagram types

  • Matrix
  • Set
  • Network diagram
  • Flowchart
  • Tree diagram
  • Graph
  • Exploded view

Specific diagram types


  • Activity diagram used in UML and SysML



  • Cartogram
  • Category theory diagrams
  • Cause-and-effect diagram
  • Circuit diagram
  • Class diagram – from UML
  • Collaboration diagram – from UML 1.x
  • Communication diagram – from UML 2.0
  • Commutative diagram
  • Component diagram – from UML
  • Composite structure diagram – from UML
  • Concept map
  • Context diagram
  • Contour diagram
  • Cross-functional flowchart


  • Database Model Diagram
  • Data Flow Model diagram
  • Data-structure diagram
  • Dependency diagram
  • Deployment diagram – from UML
  • Dot and cross diagram


  • Entity-Relationship diagram (ERD)
  • Euler diagram
  • Express-G
  • Extended Functional Flow Block Diagram (EFFBD)




  • Internal Block Diagram (IBD) used in SysML
  • IDEF0
  • IDEF1 (entity relations)
  • Interaction Overview diagram – from UML
  • Ishikawa diagram


  • Jackson diagram
  • Johnston diagram


  • Karnaugh map


  • Line of balance


  • Martin ERD
  • Mind map – used for learning, brainstorming, memory, visual thinking and problem solving


  • N2
  • Nassi-Shneiderman diagram or structogram – a representation for structured programming
  • Nomogram



  • Package diagram from UML and SysML
  • Parametric diagram from SysML
  • PERT
  • Petri net – shows the structure of a distributed system as a directed bipartite graph with annotations
  • Piping and instrumentation diagram (P&ID)
  • Phase diagram
  • Pourbaix diagram
  • Process Flow diagram or PFD – used in chemical engineering
  • Program Structure diagram


  • Requirement Diagram Used in SysML
  • Rich Picture


  • Sankey diagram - represents material, energy or cost flows with quantity proportional arrows in a process network.
  • Sentence diagram -- represents the grammatical structure of a natural language sentence.
  • Sequence diagram from UML and SysML
  • SDL/GR diagram – Specification and Description Language. SDL is a formal language used in computer science.
  • Shlaer-Mellor – used in software engineering
  • Smith chart
  • Spider Chart
  • SSADM – Structured Systems Analysis and Design Methodology (used in software engineering)
  • State diagram from UML and SysML
  • Swim lane
  • System context diagram
  • System structure
  • Systematic layout planning


  • Timing diagram
  • TQM diagram
  • Tree Diagram


  • UML diagram – Unified Modeling Language (used in software engineering)
  • Use case diagram – from UML and SysML


  • Value stream mapping
  • Venn diagram
  • Voronoi diagram




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