The cartographer selects a symbol form, and varies its size from place to place, in proportion to the quantities the symbol represents. The map reader forms a picture of the quantitative distribution by examining the pattern of the different sized symbols.
"River characteristics. The area of the circle is proportional to the channel width. The color of the large circle approximates the color of the water (gray indicates no color was mentioned in the journals). Descriptions of the bed material are determined by the position of the solid black circle within the black triangle. The example in the upper right indicates a width of 500 yards, a yellow water color, and bed material that is mostly sand with some gravel and some mud."
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