There are 6 main types of graphs used to present data: 1) pictographs use pictures to represent data simply for small numbers, 2) bar graphs use columns to compare bigger numbers and categories, 3) double bar graphs compare sets of data by grouping results for the same category, 4) circle graphs/pie charts represent proportions as percentages to compare samples of different sizes, 5) line graphs track values measured at intervals over time, and 6) double line graphs have two or more lines on the same graph. The best graph type depends on the purpose and amount of data being presented.