Meaningful differences between lines appearing in graphic displays, such as flow paths, should be depicted by using various line types, e.g., solid, dashed, dotted, and widths.
Additional Information:
Three or four line types may be readily distinguished, and two or three line widths may be readily distinguished. A line displayed on a VDU will appear continuous if the separation between resolution elements is less than one minute of arc. To provide the illusion of continuity, graphic lines should contain a minimum of 50 resolution elements per inch.