Map symbol

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In this map, the city points, highway lines, and the fill colors of the ocean and different countries are all considered map symbols. These symbols show location, convey information, increase aesthetic appeal, and create a gestalt order to the map. India roadway map (cropped).png
In this map, the city points, highway lines, and the fill colors of the ocean and different countries are all considered map symbols. These symbols show location, convey information, increase aesthetic appeal, and create a gestalt order to the map.

A map symbol or cartographic symbol is a graphical device used to visually represent a real-world feature 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.

Contents

Map symbols simultaneously serve several purposes:

Representing spatial phenomena

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. [1] Phenomena can be categorized a number of ways, but two are most relevant to symbology: ontological form and dimensionality. When a symbol is representing a property of the phenomenon as well as its location, the choice of symbol also depends on the nature of that property, usually classified as a Level of measurement.

Ontological form

Geographic phenomena can be categorized into objects , which are recognizable as a unified whole with a relevant boundary and shape; and masses, in which the notion of boundary and wholeness are not relevant to their identity. Features such as buildings, cities, roads, lakes, and countries are geographic objects that are often portrayed on maps using symbols. Mass phenomena include air, water, vegetation, and rock. These are rarely represented directly on maps; instead, map symbols portray their properties, which usually take the form of geographic fields, such as temperature, moisture content, density, and composition.

Dimensionality

The number of spatial dimensions needed to represent a phenomenon determine a choice of Geometric primitive; each type of geometric primitive is drawn with a different type of visual symbol. [2]

Dimensions of Map Symbols
ShapeDimensionsGeometric PrimitiveSymbol Elements, Visual Variables
Point0CoordinateMarker (shape, size, color, opacity)
Line/Curve1Polyline (linear or curved segments)Stroke (color, size/weight, opacity, texture)
Planar Region/Field2Polygon, RasterBoundary Stroke

Fill (color, opacity, texture)

Volumetric Region/Field3Polygon Mesh, RasterSurface (color, size/weight, opacity, pattern)

Interior (color, opacity, texture)

The dimensionality of a map symbol representing a feature may or may not be the same as the dimensionality of the feature in the real world; discrepancies are the result of cartographic generalization to simplify features based on purpose and scale. 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. [3]

Level of Measurement of Property

Many map symbols visualize not just the location and shape of a geographic phenomenon, but also one or more of its properties or attributes. Geographers and cartographers usually categorize properties according to the classification system of Stanley Smith Stevens, or some revision thereof, such as that of Chrisman. [4] Different kinds of symbols and visual variables are better at intuitively representing some levels than others, especially when the visual variable portrays the same kind of differences as the represented attribute. [3]

Property Levels and Map Symbols
LevelDistinctionPreferred Visual VariablesSecondary Visual VariablesMap Examples
NominalSame or differentColor Hue, Shape, Texture/ArrangementOwner, Facility type
HierarchicalQualitative amount of differenceColor HueShape, ArrangementLanguages, Geologic formation
OrdinalOrderColor value, Color saturationSize, Color Hue Socioeconomic status (rich, middle class, poor)
IntervalQuantitative amount of differenceColor valueSize, Color saturation, Opacity, Hue Temperature, Year
RatioProportional differenceSize, Color value, Texture densityOpacityPopulation growth rate, population density
Cyclical [4] Angular differenceColor hue, orientationDay of the year, Aspect of terrain
Amount/Count [4] Total numberSizeColor value, OpacityPopulation, Total Income

Cognition and semiotics

The dark green patch on this map is an ad hoc symbol for the country of Poland. Locator map of Poland.svg
The dark green patch on this map is an ad hoc symbol for the country of Poland.

In cartography, the principles of cognition are important since they explain why certain map symbols work. [5] In the past, mapmakers did not care why the symbols worked. This behaviorist view treats the human brain like a black box. Modern cartographers are curious why certain symbols are the most effective. This should help develop a theoretical basis for how brains recognize symbols and, in turn, provide a platform for creating new symbols.

According to semiotics, specifically the Semiotic theory of Charles Sanders Peirce, map symbols are "read" by map users when they make a connection between the graphic mark on the map (the sign), a general or specific concept (the interpretant), and a particular feature of the real world (the object or referent). Map symbols can thus be categorized by how they suggest this connection: [6] [7]

Visual variables

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." [8] Bertin identified seven main categories of visual variables: position, size, shape, value, color, orientation, and texture/grain. [9] Since then, cartographers have modified and expanded this set. [10]

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. [11] The most common set of visual variables, as canonized in cartography textbooks and the Geographic Information Science and Technology Body of Knowledge, [3] includes the following:

National Park standard point symbols, using shape to represent different types of facilities, a nominal variable. Sample-national-park-service-pictographs.gif
National Park standard point symbols, using shape to represent different types of facilities, a nominal variable.
The synergy of Saturation (color vs. gray), value (dark vs. light), and position (centrality) to strongly establish figure-ground and visual hierarchy COL orthographic (San Andres and Providencia special).svg
The synergy of Saturation (color vs. gray), value (dark vs. light), and position (centrality) to strongly establish figure-ground and visual hierarchy
Transparency is used effectively here to indicate overlapping sovereignty claims. India Pakistan China Disputed Areas Map.png
Transparency is used effectively here to indicate overlapping sovereignty claims.

Cartographers have also proposed analogous sets of controllable variables for animated maps, [14] [2] haptic (touch) maps, [15] and even the use of sound in digital maps. [16]

Visual hierarchy

An important factor in map symbols is the order in which they are ranked according to their relative importance. This is known as intellectual hierarchy. The most important hierarchy is the thematic symbols and type labels that are directly related to the theme. Next comes the title, subtitle, and legend. [1] The map must also contain base information, such as boundaries, roads, and place names. Data source and notes should be on all maps. Lastly, the scale, neat lines, and north arrow are the least important of the hierarchy of the map. From this we see that the symbols are the single most important thing to build a good visual hierarchy that shows proper graphical representation. When producing a map with good visual hierarchy, thematic symbols should be graphically emphasized. A map with a visual hierarchy that is effective attracts the map user's eyes to the symbols with the most important aspects of the map first and to the symbols with the lesser importance later.

Map legend

The legend of the map also contains important information and all of the thematic symbols of the map. Symbols that need no explanations, or do not coincide with the theme of the map, are normally omitted from the map legend. Thematic symbols directly represent the maps theme and should stand out. [17]

See also

Related Research Articles

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<span class="mw-page-title-main">Cartogram</span> Map distorting size to show another value

A cartogram is a thematic map of a set of features, in which their geographic size is altered to be directly proportional to a selected variable, such as travel time, population, or Gross National Product. Geographic space itself is thus warped, sometimes extremely, in order to visualize the distribution of the variable. It is one of the most abstract types of map; in fact, some forms may more properly be called diagrams. They are primarily used to display emphasis and for analysis as nomographs.

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<span class="mw-page-title-main">Figure-ground (cartography)</span> Focus of attention on features in a map

Figure-ground contrast, in the context of map design, is a property of a map in which the map image can be partitioned into a single feature or type of feature that is considered as an object of attention, with the remainder of the map being relegated to the background, outside the current focus of attention. It is thus based on the concept of figure–ground from Gestalt psychology. For example, in a street map with strong figure-ground contrast, the reader would be able to isolate and focus attention on individual features, like a given street, park, or lake, as well as layers of related features, like the street network.

<span class="mw-page-title-main">Choropleth map</span> Type of data visualization for geographic regions

A choropleth map is a type of statistical thematic map that uses pseudocolor, meaning color corresponding with an aggregate summary of a geographic characteristic within spatial enumeration units, such as population density or per-capita income.

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<span class="mw-page-title-main">Map coloring</span> Differentiating different features of a map using different colours.

In cartographic design, map coloring is the act of choosing colors as a form of map symbol to be used on a map.

<span class="mw-page-title-main">Thematic map</span> Type of map that visualizes data

A thematic map is a type of map that portrays the geographic pattern of a particular subject matter (theme) in a geographic area. This usually involves the use of map symbols to visualize selected properties of geographic features that are not naturally visible, such as temperature, language, or population. In this, they contrast with general reference maps, which focus on the location of a diverse set of physical features, such as rivers, roads, and buildings. Alternative names have been suggested for this class, such as special-subject or special-purpose maps, statistical maps, or distribution maps, but these have generally fallen out of common usage. Thematic mapping is closely allied with the field of Geovisualization.

<span class="mw-page-title-main">Multivariate map</span> Thematic map visualizing multiple variables

A bivariate map or multivariate map is a type of thematic map that displays two or more variables on a single map by combining different sets of symbols. Each of the variables is represented using a standard thematic map technique, such as choropleth, cartogram, or proportional symbols. They may be the same type or different types, and they may be on separate layers of the map, or they may be combined into a single multivariate symbol.

<span class="mw-page-title-main">Visual hierarchy</span> Visual design technique to convey importance

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<span class="mw-page-title-main">Flow map</span> Thematic map visualizing linear flow

A flow map is a type of thematic map that uses linear symbols to represent movement between locations. It may thus be considered a hybrid of a map and a flow diagram. The movement being mapped may be that of anything, including people, highway traffic, trade goods, water, ideas, telecommunications data, etc. The wide variety of moving material, and the variety of geographic networks through they move, has led to many different design strategies. Some cartographers have expanded this term to any thematic map of a linear network, while others restrict its use to maps that specifically show movement of some kind.

<span class="mw-page-title-main">Dot distribution map</span> Thematic map using dots to visualize distribution

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<span class="mw-page-title-main">Map layout</span> Arrangement of map elements on a page

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<span class="mw-page-title-main">Chorochromatic map</span> Thematic map visualizing a discrete field

A Chorochromatic map, also known as an area-class, qualitative area, or mosaic map, is a type of thematic map that portray regions of categorical or nominal data using variations in color symbols. Chorochromatic maps are typically used to represent discrete fields, also known as categorical coverages. Chorochromatic maps differ from choropleth maps in that chorochromatic maps are mapped according to data-driven boundaries instead of trying to make the data fit within existing, sometimes arbitrary units such as political boundaries.

A visual variable, in cartographic design, graphic design, and data visualization, is an aspect of a graphical object that can visually differentiate it from other objects, and can be controlled during the design process. The concept was first systematized by Jacques Bertin, a French cartographer and graphic designer, and published in his 1967 book, Sémiologie Graphique. Bertin identified a basic set of these variables and provided guidance for their usage; the concept and the set of variables has since been expanded, especially in cartography, where it has become a core principle of education and practice.

<span class="mw-page-title-main">Cartographic design</span> Process of designing maps

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<span class="mw-page-title-main">Typography (cartography)</span> Text used to label maps

Typography, as an aspect of cartographic design, is the craft of designing and placing text on a map in support of the map symbols, together representing geographic features and their properties. It is also often called map labeling or lettering, but typography is more in line with the general usage of typography. Throughout the history of maps to the present, their labeling has been dependent on the general techniques and technologies of typography.

<span class="mw-page-title-main">Proportional symbol map</span> Thematic map based on symbol size

A proportional symbol map or proportional point symbol map is a type of thematic map that uses map symbols that vary in size to represent a quantitative variable. For example, circles may be used to show the location of cities within the map, with the size of each circle sized proportionally to the population of the city. Typically, the size of each symbol is calculated so that its area is mathematically proportional to the variable, but more indirect methods are also used.

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