To understand a bar graph you must identify the meaning assigned to each axis. The line running north and south on the left part of the graph should be labeled with numbers. These numbers may represent units such as hits or home runs. They may measure votes received. They could measure years or other time-related data. At the base of the graph you should label what each bar represents. They could be individual players, teams, products or candidates. Whatever the case, identify the meaning of each axis.
Record data for each bar. With this information you can determine the comparative performance of each person or group represented by the bar. You can tell how many more home runs player A had compared to player B. You can tell by how many votes a candidate won an election. It becomes obvious which album had a greater increase in record sales over the past year. By interpreting the data in the bar graph, the comparative chart serves its practical purpose.
Use a pie graph to illustrate the sales of your product compared to two of the closest competitors. This helps visualize what percentage of the buyers are purchasing your product compared to that of the competition. By coloring in each segment of the market share, the results are more visible. If three soda companies were charted, the pie graph would show that Coca Cola sold 62% of all beverages sold, Pepsi Cola claimed 35% and the final 3% were sold by RC Cola.
In general, bar graphs work best with whole number totals for quantitative analysis. Pie graphs work better where percentages are being considered. These can be applied and used in educational, business, marketing and social science areas.