Map symbol

Lore & Background

Map symbols are used to represent geographic phenomena, which exist in and are represented by a variety of spatial forms. Different kinds of symbols are used to portray different spatial forms. Phenomena can be categorized by ontological form—objects such as buildings, cities, roads, lakes, and countries, and masses such as air, water, vegetation, and rock—and by dimensionality, which determines a choice of geometric primitive. The dimensionality of a map symbol may or may not match the real-world feature due to cartographic generalization; for example, a three-dimensional road is often represented as a one-dimensional line symbol, while two-dimensional cities are frequently represented by zero-dimensional points. Many map symbols visualize not just location and shape but also properties or attributes, categorized according to the classification system of Stanley Smith Stevens or a revision thereof. In cartography, principles of cognition explain why certain map symbols work. According to the semiotic theory of Charles Sanders Peirce, map symbols are read when a connection is made between the graphic mark (the sign), a concept (the interpretant), and a real-world feature (the object or referent). Symbols can be categorized by how they suggest this connection: iconic (similar appearance), functional (directly represent activity), conceptual (represent a concept), conventional (commonly used), or ad hoc (arbitrary, requiring a legend). Jacques Bertin developed the concept of visual variables in his 1967 book 'Sémiologie Graphique,' identifying seven main categories: position, size, shape, value, color, orientation, and texture/grain. Each variable may convey information, provide contrast, establish figure-ground contrast and visual hierarchy, or add aesthetic appeal. Size is effective for quantitative data; shape differentiates nominal categories; color hue differentiates nominal variables or carries psychological connotations; color value connotes ordinal measures; saturation is marginal for property information but effective for figure-ground; orientation communicates real-world orientation; and pattern or texture aggregates similar symbols into a composite.

Reader's Guide

Map symbols are fundamental to cartography, serving as the primary means of translating geographic phenomena into visual representations. Their significance lies in their ability to simultaneously declare existence, show location and extent, visualize attribute information, contribute to aesthetic appeal, and establish visual hierarchy. The categorization of symbols by ontological form and dimensionality allows cartographers to match symbol type to the nature of the phenomenon, while the level of measurement of properties guides appropriate visual variable selection. The semiotic framework of Charles Sanders Peirce provides a theoretical basis for understanding how map readers interpret symbols, distinguishing between iconic, functional, conceptual, conventional, and ad hoc symbols. Jacques Bertin's visual variables—position, size, shape, value, color, orientation, and texture/grain—remain a core framework for symbol design, with each variable having specific strengths for conveying different types of information. The legacy of map symbols extends beyond traditional paper maps into digital geographic information systems, where the same principles apply to interactive and dynamic mapping. Understanding cognition and semiotics helps modern cartographers develop more effective symbols, moving beyond the behaviorist view that treated the human brain as a black box. The ongoing refinement of visual variables and symbol categories continues to shape how geographic information is communicated to diverse audiences.

Did You Know?

• Map symbols can be categorized by how they suggest a connection between the graphic mark, a concept, and a real-world feature: iconic, functional, conceptual, conventional, or ad hoc.
• The dimensionality of a map symbol may differ from the real-world feature due to cartographic generalization; for example, a three-dimensional road is often represented as a one-dimensional line symbol.
• Jacques Bertin identified seven main categories of visual variables in his 1967 book 'Sémiologie Graphique': position, size, shape, value, color, orientation, and texture/grain.
• Color saturation has been found to be of marginal value in representing property information but is very effective at establishing figure-ground and visual hierarchy.

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