Bar graphs can show several kinds of relationships, including comparisons, trends, and distributions. Like line graphs, bar graphs are drawn from a series of values plotted on two axes, but the values are represented by vertical or horizontal bars instead of points joined by a line. Because each bar represents a separate quantity, bar graphs are especially appropriate when the data consist of distinct units, such as tons of grain or megawatts of hydroelectric power produced over a specified period.

Commonly used bar graphs include a simple bar graph, subdivided bar graph, and subdivided 100-percent bar graph.

The following figures illustrate how the same data plotted on these three kinds of bar graphs can create quite a different appearance for readers.

In the simple bar graph, all bars represent the same type of information, so the differences are stressed. The same guidelines apply to any bar graph:

• Make bars the same width.

• Make the space between bars one-half the bar width.

• Label each bar.

In the subdivided bar graph, each bar is subdivided to represent the magnitude of different components. Parts are differentiated by shading or crosshatching. Although the total magnitude of each bar can be compared, as in a simple bar graph, the individual components are not easily compared.

In the subdivided 100-percent bar graph, each bar extends to 100 percent, and the components of the bar are separated by percentage. Unlike simple bar graphs and subdivided bar graphs that enable you to compare total magnitude, subdivided 100-percent bar graphs enable easy comparison of the individual components.

Other variations of bar graphs-subdivided 100-percent area graph, multiple bar graph, sliding bar graph, and floating bar graph-are appropriate for somewhat more complex displays of information.

The following figure illustrates a variation of a subdivided 100-percent bar graph-a subdivided 100-percent area graph. Imagine a series of 150 bars, each extended to 100 percent and each bar subdivided to show the percentage of, say, types of fuel used during one year. The bars are then pushed together so the overall effect is a continuous line for each category. The area under each bar is shaded to make the distinctions clear.

A multiple bar graph groups two or more bars to present the magnitude of related variables. The example in below compares "Feature X" and "Feature Y" over an 8-year period.

The bars in the sliding bar graph in the following figure move along an axis that is usually marked in opposing values (active/passive, hot/cold) that extend on either side of a central point, such as values on a temperature scale.

The floating bar graph in the figure below has bars that "float" in the area above the x-axis, which may extend below zero.