Charts and graphs are a means of displaying information in a way that's easy to digest. Through lines, bars or other visual representations, both charts and graphs illustrate relationships between sets of data so that anyone can understand them. Even though charts and graphs are often used in the same sentence to explain the illustration of data, the terms are not interchangeable. Charts and graphs illustrate relationships between data in different ways.
Relationships Over Time
Graphs, especially line graphs, are best for illustrating a trend over time. For example, you could use a line graph to show the population increase or decrease in an urban neighborhood over 20 years. Charts cannot show this relationship as well, since they use a series of bars, rather than data points connected by a line that goes up and down. Graphs are much better at showing trends for a single set of data than charts are.
Charts are useful for displaying patterns or information about frequency. The bars on a chart are higher or longer depending on the value they represent. For example, a chart can be used to show the total sales of three different products, such as three competing brands of paper towels. A line graph wouldn't show the relationship between these variables correctly. Since the products are different, it wouldn't make sense to draw a line that connects them. A chart, on the other hand, might reveal that Brand X sells significantly more than Brand Y.
It's not possible to use a graph to show proportions or percentages. However, pie charts, a specific type of chart, can do this well. Pie charts compare parts to a whole, so they can show proportional relationships. For example, pie charts might record the population's opinions on a given issue. The pie chart would show the percentage who were for the issue, those against it, and those who were undecided. It's possible to record this information on a bar graph as well, but the difference between the percentages wouldn't be as easy to connect.