Selecting which Type of Graph or Chart to Use
- Some messages are shown more clearly with one kind of graph than with others. To show change over time, one might choose to use a line graph. The sample line graph shows a change each year in the number of trees planted by two schools between 1999 and 2003. A bar graph could also show this increase, but a line graph may show this change over time more clearly.
- Graphs sometimes make us think about information in new ways. Imagine a line graph showing two different changes during the same period and in the same place. We wonder if one change might have caused the other.
Bar Graphs and Pictographs
- Bar graphs and pictographs can be effective to show how one measured value (or number fact) compares to another. For example, the purpose might be to show the number of trees the fourth grade planted on Arbor Day in 2002 and 2003 and how that value compares with the number of trees students from other grades planted.
- On the bar graph, the tallest bar represents the most trees. In the sample bar graph, the reader can tell which grade planted the most trees in both 2002 and 2003. The label under the tallest bar shows it.
- On a pictograph for the same data, instead of drawing different sized bars, students might draw different sized trees. They could even cut pieces of green construction paper, or magazine pictures, or photos, then glue them to form a collage illustration of different sized trees. The tallest tree picture, of course, would represent the most trees planted. The label under the tallest tree would tell which grade planted the most trees.
- A pie chart-type graph illustrates parts of a whole. A pie chart might describe kinds of trees planted. It could show what part (fraction or percent) of all the trees were pines, apple trees, dogwoods, and junipers.
- When planning the budget for a project, a pie chart could be helpful to show what part of project money would be used for each expense. Also, a class could make a pie chart to show the plan for budgeting time.
- Students can look in mathematics books and ask mathematics teachers for guidance if they have questions about how to make graphs.