3) Simplicity: As one part of 3D GIS visualization, 3D
symbolic model should inherit the traditional map in most
areas. Symbol’s clarity and simplicity is the basic condition to
ensure maps to read easily. 3D symbolic model should also be
clear and easy to read, so 3D symbolic model should be brief
and clear, and formed by a minimum of a simple shape. The
volume of model can not be too large and the various
components should be compact. It is one of the prerequisites to
ensure the symbolic model of simplicity for minimize the time
occupied by the light calculation and improving the speed of
graphical display.
4) Feasibility: Hardware and software support must be
taken into account when Symbols are designed. If too many
polygons are in a symbol, it will consume a large amount of
computing time for light calculation. Then this symbol design
is a failure