Symbolization

Symbolization is the process of linking geographic phenomena (i.e., real-world features and thematic data) to the graphic marks on a map. Everything seen on a map is a graphic mark. Graphic marks include point, line, area, and volumetric symbols. For example, a graphic mark in the shape of a cross might represent a hospital or in the shape of a bold red line might represent a political boundary or in the shape of a blue area might represent a lake. The goal of symbolization is to imbibe the graphic marks with meaning, that is, to have the marks portrayed so that they authentically represent or “stand for” geographic phenomena, such as schools, highways, counties, elevations, and population distributions and densities.

Symbols can be classified as either pictographic or abstract. Pictographic symbols represent real-world, tangible features such as houses, roads, rivers, and coastlines and are designed to look like or replicate the feature they are designed to represent. Abstract symbols generally take the form of a geometric shape, such as a circle, square, triangle, sphere, or column. They can represent real-world features, for example, a square for a house, but they are more often used to show the spatial variation in the quantities of a geographic variable, such as population densities and other abstract, statistical surfaces. Maps that utilize abstract symbolization, such as choropleth, graduated symbol, and isarithm maps, require a well-designed legend to describe the symbols and their associated amounts.

Symbolization requires the generalization of real-world geographic phenomena. It is heavily influenced by the scale of the map, wherein a smaller-scale map requires greater generalization. The result is that feature symbols are not drawn to scale and they may be of different dimensions than those of the real-world features they represent. For example, symbols are often drawn larger than the size that the corresponding real-world features would be if drawn to scale. Examples of this are rivers and roads that are typically drawn wider than they would be drawn if at scale, so that they will be visible on the map. In addition, at a large scale, the boundary of a city might be drawn as it appears in the real world, whereas the city might be reduced to a dot at a smaller scale.