A bar graph (also known as a Pareto Diagram) is a chart that contains horizontal or vertical bars.
Each bar represents a category of data (but not specific data). Since qualitative variables have no uniform distance between levels, this makes their discrete nature well suited for bar graphs. Either axis can display the specific categories being compared.
The arrangement of the categories (bars) and the axis on which they are displayed is arbitrary and solely at the discretion of the person making the bar graph.
Line graphs are used to display comparisons between 2 variables, line graphs involve an x-axis horizontally and a y-axis vertically on a grid.