Line graphs are used to portray continuous movement or change in a measured variable, typically against a time scale. They are best for showing the trend in a set of data over time, but are less effective in comparing amounts of two variables.

• Five or six curves on one graph are usually plenty. The real number of curves that can be presented clearly on one graph depends on the position of the curves and the function of the graph.

• Use thick, solid, colored lines for projection and patterned lines for black and white printouts

• Use a different color for each line with the most important line the lightest color.

• Lines should be at least 2.5 points in order to show up well when projected.
  
  
• Curves should be the heaviest lines on the graph.
  
  
• Data points should always stand out from and dominate the connecting linework since the data points are the actual data and the connecting lines are usually just a visual device to show trends and continuity.

Good Example

Poor Example

• Symbols and connecting lines should dominate all other elements of a chart.

• Symbol diameter should be about two to three times the width of any connecting lines.

• Polygon symbols should be used as markers or symbols. Recommended symbols are filled circle, triangle, and square, and open circle, triangle, and square. Other symbols are not as distinctive and if used, they should be carefully oriented so that they can be distinguished from the recommended ones and from the connecting line. Avoid X’s, crosses or symbols with dots.

• For data points that overlap, the symbols should be drawn overlapped.

• All symbols should look the same size.

• Curves should not extend before the first data point or after the last data point.

• Identify curves with a brief label next to them. Place the label close to the curve. It should be contained within the rectangle implied by the axes and should be oriented horizontally.

• Don’t use arrow or leader lines as they clutter the graph.