Cartographic Symbol Basics:

Data depicted on maps are symbolic representations of geographic phenomena found on the earth’s surface

Only at a scale of 1:1 could physical data be depicted at its true size and in complete detail, but this scale is rarely practical and as such all features and thematic data shown on a map must undergo a process of simplification, generalization (sometimes exaggeration), and finally symbolization.

In effect, maps are complex tools for visualizing and communicating scaled-down geospatial data, and graphic symbology is their language of communication.

Geographic phenomena:

Geographic phenomena that are mapped involve location, distance, volume, movement, function, process, correlation, etc.

The Geographic phenomena can be classified into four basic categories for mapping.

1. POINT (non-dimensional) data

2. LINE (one-dimensional) data

3. AREA (two-dimensional) data and…

4. VOLUME (three-dimensional data),

The four categories of data must be represented on maps by only three basic symbol types: point, line, and area. Therefore, considerable imagination must be used to design map symbols that portray more than one data characteristic at the same time.

1. A point symbol represents a geographic feature or event characterized by location and attributes. Its location can be represented by a single "x,y" coordinate pair, while attributes can be many. For example, a populated place or a mine site can be represented by a point symbol. 

2. A line symbol represents a geographic feature characterized by linear dimension, but not area. In digital technology, a line is a sequence or stream of point coordinates with a node at each end (vector data) that symbolizes a linear feature such as a road, river, or boundary. 

3. An area symbol represents a closed geographic surface feature, two-dimensional geometric region, or a polygon. A census division, a lake or a province are examples of area features. 

Symbology typically found on a topographic map:

(From Topographic Maps...The Basics, Centre for Topographic Information, Natural Resources Canada).

Symbol design:

Once the purpose of a map has been established, it is necessary to select which geographical features are to be depicted on the map, and in what manner.

Map scale is an important factor in determining which features can be shown and how. Some data are not suitable for depiction at all scales. If displayed at the wrong scale, data may appear too congested or too sparse.

Map Symbols Designs

In general, there are two basic symbol designs that may be used to portray information on maps, pictorial and abstract. Symbols that are pictorial look like the features that they represent. These symbols tend to reflect the shape and color of the feature. For example, the symbol for a picnic site may be a picnic table, or the symbol for a vegetated area may be a green polygon.

Symbols described as abstract may be any geometric shape assigned to represent a feature. For example, a series of graduated dots and/or squares could represent populated places on a reference map. On the other hand, colored or patterned polygons could represent varying concentrations of people, on a population density map.

There is little difference in the way symbols are designed for display in the computer environment and for the traditional paper map. The main concerns with the computer mapping environment are screen resolution, map scale, and color.

With regard to screen resolution, the smallest size for displaying a symbol is determined by the size of a physical pixel on the monitor. Objects that are smaller than the pixel resolution cannot be displayed on a computer monitor.

In regard to map scale, problems can arise in the sizing of symbols. A symbol designed to be legible on a small scale map may appear too small when the map is viewed at a larger scale. On the other hand, a symbol sized to look correct at a large scale may appear exaggerated at a smaller scale.

Please note that on any map, regardless of symbol design or the media used, all symbols must be clearly explained in the map legend. 

Color and Map Symbols

For ease of identification, map symbols have distinctive colors

1. Black – manmade (roads, buildings, mines)

2. Red – to distinguish significant manmade

features (e.g. highways)

3. Blue – drainage features (seas, oceans, lakes,

rivers, ponds)

4. Green – Vegetation (forests, grasslands)

5. Brown – Elevation (contour lines showing

mountains, hills)

6. Purple – shows recent revisions of the map.