A symbol is a graphic pattern that is used to represent a feature on a map. According to the type of features they represent, symbols are classified into marker symbols (representing point and node features), line symbols (representing arcs, routes, etc), shade symbols (to fill polygons and regions with solid colour or shade patterns) and text symbols (representing text used to label features).
Symbols on a map are either points, lines or areas. Each symbol might differ in size, shape, density, texture, orientation and colour. A poor match between the real world and the symbol used to depict it can confuse the user regarding its true nature. Colour is important in influencing the user's understanding of the map. The overall impact of the map can be affected by colour and symbolism. Black and white maps use differently shaped symbols and shading patterns are effective for simple patterns while being easier and cheaper to reproduce. Colour maps are used to effectively represent complex spatial patterns. The shape and pattern of symbolism used should bear relation to the feature being represented.
Careful choice of shape and pattern of symbolism used can influence the user's impression of the map. Density and texture of shading can affect the impression given by the map. To ensure correct interpretation, the map user is given the necessary information by a key or legend. A key tells the user what the shading patterns, colours, line and point symbols mean.
Intellectual objectives and visual objectives of map design are sometimes in conflict. Symbols on the map (logical and aesthetic) dictate a consistent approach. Cartographers have established (over a period of generations) an exhaustive set of conventions and traditions to deal with such cases. These conventions were a result of trial and error and testing among map users. They act as guidelines for cartographic representations.