This is ambiguous in a triaxial-graph, where the directionality of the axes depends on whether viewed from inside or outside the graph. The USDA soil texture triangle is usually portrayed so that values on all axes increase in the clockwise direction. It is also necessary to place the three variables in a consistent arrangement. The author proposes that red be assigned to clays, blue to sand, and green to silt. Establishing cartographic conventions for the color assignments, directionality of axes, and placement of variables is essential for the consistent representation of data.
Inconsistency can only increase user confusion.
While the traditional soil texture classification system has proven itself useful for many purposes, it is necessary to recognize the arbitrary nature of textural classification. There is no single standard for defining the size range of sand, silt and clay particles. While the color legend proposed here can be used in different parts of the world, it will have somewhat different meaning in different regions. The notion that soil texture is best described by classing particles into three broad groups is also subject to criticism. Shirazi's aspatial visualization of texture involves a bell curve, which cannot be spectrally encoded like the soil triangle.