page_title: Map symbol
section_title: Visual variables
hierarchical_section_title: Map symbol / Visual variables
caption_attribution_description: English: Composite map showing the borders of India, Pakistan &amp; China as per official sources overlaid on areas of actual administrative control. Areas where official borders intersect are disputed areas administered by one country and claimed by another country. Each disputed region is indicated by a circle representative of its area with the color of the administering country and outlined by the color of the claimant country.
context_page_description: A map symbol is a graphical device used to visually represent a real-world phenomenon or a characteristic thereof on a map, working in the same fashion as other forms of symbols. Map symbols may include point markers, lines, regions, continuous fields, or text; these can be designed visually in their shape, size, color, pattern, and other graphic variables to represent a variety of information about each phenomenon being represented.
  Map symbols simultaneously serve several purposes:
  Declare the existence of geographic phenomena
  Show location and extent
  Visualize attribute information
  Add to the aesthetic appeal of the map, and/or evoke a particular aesthetic reaction
  Establish an overall gestalt order to make the map more or less useful, including visual hierarchy
context_section_description: A map symbol is created by altering the visual appearance of a feature, whether a point, line, or region; this appearance can be controlled using one or more visual variables. Jacques Bertin, a French cartographer, developed the concept of visual variables in his 1967 book, "Sémiologie Graphique."  Bertin identified seven main categories of visual variables: position, size, shape, value, color, orientation, and texture/grain. Since then, cartographers have modified and expanded this set.
  Each of these variables may be employed to convey information, to provide contrast between different features and layers, to establish  figure-ground contrast and a clear visual hierarchy, or add to the aesthetic appeal of the map. The most common set of visual variables, as canonized in cartography textbooks and the Geographic Information Science and Technology Body of Knowledge, includes the following:
  Size, how much space a symbol occupies on a map, most commonly refers to the area of point symbols, and the thickness of line symbols, although the cartogram controls the size of area features proportional to a given variable. Size has been shown to be very effective at conveying quantitative data, and in the visual hierarchy.
  Shape is most commonly discussed in the context of point symbols (as the shapes of lines and areas are typically fixed by geographic reality), and is generally only used to differentiate nominal categories. That said, some maps purposefully manipulate the shape of lines and areas, often for purposes of Cartographic generalization, such as in schematic transit maps, although this distortion is rarely used to convey information, only to reduce emphasis on shape and location.
  Color Hue is the visual property caused by the blending of various wavelengths of light, which we commonly refer to by color names like "red," "green," or "blue." Maps often use hue to differentiate categories of nominal variables, such as land cover types or geologic layers, or for its  psychological connotations, such as red implying heat or danger and blue implying cold or water.
  Color value or lightness, how light or dark an object appears. Value effectively connotes "more" and "less," an ordinal measure; this makes it a very useful form of symbology in thematic maps, especially choropleth maps. Value also contributes strongly to Visual hierarchy; elements that contrast most with the value of the background tend to stand out most (e.g., black on a white sheet of paper, white on a black computer screen).
   Color saturation/intensity is the purity or intensity of a color, created by the degree of variety of light composing it; a single wavelength of light is of the highest saturation, while white, black, or gray has no saturation (being an even mixture of all visible wavelengths). Saturation has been found to be of marginal value in representing property information, but is very effective at establishing  figure-ground and visual hierarchy, with bright colors generally standing out more than muted tones or shades of gray.
  Orientation, the direction labels and symbols are facing on a map.  Although it is not used as often as many of the other visual variables, it can be useful for communicating information about the real-world orientation of features, such as wind direction and the direction in which a spring flows.
  Pattern or  Texture is the aggregation of large numbers of similar symbols into a composite symbol, such as a forest represented by a random scattering of tree icons. In addition to the visual variables that make up the sub-symbols, there are variables for controlling the pattern as a whole:
  Grain or Spacing, the distance between the individual symbols. Typically seen as similar to value, only with a weaker effect.
  Arrangement, the pattern of distribution of the sub-symbols, often either random or as a regular grid.
   Transparency or  Opacity, the mathematical blending of symbols of overlapping features, giving the illusion of underlying symbols being partially visible through overlying symbols. This is a recent addition due to softwar
caption: Transparency is used effectively here to indicate overlapping sovereignty claims.
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