Map symbols should be designed or chosen according to principles of logic and communication to serve as a graphic code for storing and retrieving data in a two or three dimensional geographic framework.
Appreciating the logic of map symbols begins with understanding the existence of three distinct categories, including point, line and polygons (areas).
Maps and 3D models include generally a combination of all three. These tree main categories can be further differentiated by variations in "hue" (color), "gray tone value", "texture" and "orientation", "shape" and "size".
Each of these variables or their combinations excel in portraying particular features and their variations.
When using color (hue) for characterizing areas, decoding is made simpler when darker means "more" and lighter means "less". Color conventions allow map symbols to exploit idealized associations of water with blue and forested areas with green. This the combination of the two, implies that dense primary forest is dark green, secondary forest green, and grassland light green, and that deep waters are dark blue and shallow waters light blue .
"Size" is more suited to for showing different in amount of count, whereas "variations in gray tone" are preferred for distinguishing differences in rate or intensity. Symbols varying in orientation are useful mostly for representing directional occurrences like winds, migration streams or other. Line symbols best portray water courses, roads, trails, boundaries and may combine different variables, including color and size (thickness). A heavier line readily suggests greater capacity or heavier traffic than a thin line implies.
Each symbol should be easily discernable from all others to clearly distinguish unlike features and provide a sense of graphic hierarchy. A poor match between the data and the visual variables may frustrate and confuse the map user.
While in planimetric mapmaking the only limitation in the choice of symbols is fantasy (with logic), participatory 3-D modeling (P3DM) frequently depends on the availability of materials, particularly for point features which are generally represented by push and map pins. Lines and polygons can be easily represented by color-coded yarns and different color paints.
Standardization of symbols serves for ready unambiguous recognition of features and promotes efficiency in both map production and use, exchange of data and comparison. Maps and models sharing a common graphic vocabulary are definitely more powerful in convening the intended message and decoding simpler.