UN - Geographic Information Systems
In cartography, the design elements used to represent map features. Symbol types are points, lines and polygons of a certain shape. Symbolization involves the choice of graphic variables, such as shape, size, colour, pattern and texture.
United Nations, "Handbook on Geospatial Infrastructure in Support of Census Activities", Department of Economic and Social Affairs, Statistics Division, Studies in Methods, Series F No. 103, New York, 2009