A bar graph and a line graph are two commonly used types of graphs that illustrate data visually. The main difference between the two lies in how they represent the data.

A bar graph uses rectangular bars of equal width to compare different categories or groups. The height of each bar represents the value of the data being depicted. Each bar is separate from one another and can be easily compared by their lengths. Bar graphs are particularly useful for displaying categorical data and making comparisons between different groups or categories.

On the other hand, a line graph connects data points with lines to show the relationship between two variables over time or another continuous scale. It is a useful tool for illustrating trends or changes over a specific period. Line graphs are particularly effective in visualizing data that follows a continuous sequence, such as tracking stock prices over time or displaying population growth. The line represents the overall trend and the individual data points show specific values at different time intervals.

In summary, bar graphs are used to compare different categories, while line graphs are used to show trends or changes over a continuous scale, typically over time.