A Bar Graph is a method of displaying categorical data for comparison, with one axis representing the categories and the other representing discrete values. These discrete values are a measure of frequency. These axes may be switched, resulting in two kinds of bar graphs. Bar graphs have either horizontal or vertical bars, depending on where the categorical axis is. If the categories axis is on the bottom (the x axis), the Bar graph is vertical, and if it is on the side (the y axis), then the bar graph is horizontal. Although one is referred to as a Vertical Bar Chart and the other is referred to as a Horizontal Bar Chart, they represent the same thing and are therefore display the same data, only with an adjusted orientation. It is a purely cosmetic adjustment.
Bar graphs, sometimes called bar charts, are used to compare data. The key to comparing data using a bar graph is ensuring that the same scale is used for each piece of the bar graph. By adjusting the scale, bar graphs can sometimes become misleading, demonstrating larger or smaller discrepancies than actually exist. This website has a few examples of bar graphs that are misleading, along with other kinds of misleading graphs as well.
This Site provides introductory information to bar graphs. It includes recognizing the different parts of the bar graph and also how to analyze bar graphs. It also includes sample questions to ensure you understand the graph correctly. This site includes step by step instructions as to how to construct a bar graph. This site, although brief, demonstrates the possible problems Bar charts may have and aspects of the chart to watch out for. For example, avoid comparing two charts with different scales, as mentioned earlier.