What is a Bar Graph Used For

A bar graph (also known as a bar chart or bar diagram) is a visual tool that uses bars to compare data among categories. A bar graph may run horizontally or vertically. The important thing to know is that the longer the bar, the greater its value.

Bar graphs consist of two axes. On a vertical bar graph, the horizontal axis (or x-axis) shows the data categories. The vertical axis (or y-axis) is the scale. The colored bars are the data series.

Bar graphs have three key attributes:

- A bar diagram makes it easy to compare sets of data between different groups at a glance.
- The graph represents categories on one axis and a discrete value in the other. The goal is to show the relationship between the two axes.
- Bar charts can also show big changes in data over time.

Bar Graph vs Line Graph

Bar graphs display data in a way that is similar to line graphs. Line graphs are useful for displaying smaller changes in a trend over time. Bar graphs are better for comparing larger changes or differences in data among groups.

When to Use a Bar Graph

Bar graphs are an effective way to compare items between different groups. This bar graph shows a comparison of numbers on a quarterly basis over a four-year period of time. Users of this chart can compare the data by quarter on a year-over-year trend, and also see how the annual sales are distributed throughout each year.

Bar graphs are an extremely effective visual to use in presentations and reports. They are popular because they allow the reader to recognize patterns or trends far more easily than looking at a table of numerical data.

Types of a Bar Graph

When presenting data visually, there are several different styles of bar graphs to consider.

Vertical Bar Graph

The most common type of bar graph is the vertical bar graph. It is very useful when presenting a series of data over time. The vertical bar chart below shows a series of quarterly data, categorized by year. The reader can easily see not only the trends of sales over the four-year period, but also how the sales compare during each quarter.

One disadvantage of vertical bar graphs is that they don’t leave much room at the bottom of the chart if long labels are required.

Horizontal Bar Graph

Converting the vertical data to a horizontal bar chart solves this problem. There is plenty of room for the long label along the vertical axis, as shown below.

Stacked Bar Graph

The stacked bar graph is a visual that can convey a lot of information. Look at the stacked bar graph below, and you can see that there are eight data series (world regions) within each category (year).

Trying to show all of these data series in a standard bar chart would be impractical. The stacked bar chart in this example allows us to pick out three important facts:

- The total population is increasing dramatically over the time period displayed.
- The largest region is the purple segment—Non-OECD Asia—which is also increasing very rapidly.
- Africa, represented by the gold band second from the top, is clearly the second-largest region and has a rapidly growing population.

One of the disadvantages of a stacked bar chart is that may not show data in as clear a manner as intended, and if not read carefully, might even be misleading. For example, in the above chart, the population of Africa increased more than 100% during this time period while the population of Non-OECD Asia increased by about 50%. Perhaps lost in this chart is that the population of the Middle East also grows by more than 100%.

The point is to make sure that you select the type of graph that best presents the data you want to emphasize.

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