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.
The term diagram
Diagram has two meanings in common sense.
- 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.
- 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". 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.
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.
Diagrams and charts, in contrast to computer graphics
, technical illustrations, infographics
, maps, and technical drawings
, show abstract
rather than literal
representations of information. In essence diagrams are:
- 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. 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.
Diagrams and charts are very good at showing actions
. 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.
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.
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 there 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
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
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
- 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
- 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.