When you want to see how one amount compares to other amounts, or to identify and measure the parts of a whole, a chart can be a good source of information. This chart, for example, shows what percentage of land each country got when Catherine the Great split up Poland. As you can see when you compare the pieces of this pie, Catherine got the best deal in the partition of Poland. Charts like these, especially when combined with maps, can help you draw conclusions, make judgments, and see the bigger picture related to an event.

Graphs are useful when you're trying to show how information changes over time. As you might remember from math class, graphs have at least two axes: the X axis, which goes horizontally (side to side), and the Y axis, which goes vertically (up and down). In the graph below, you can see how much cargo and how many ships have gone through the Panama canal over the years. The X axis here shows the years (starting in 1980 and ending in 2005), while the left Y axis marks the weight that moved through the canal over a period of 25 years and the right Y axis shows the number of ships that sailed through the canal in this time. If you compare these two lines, you'll see a close--but not perfect--relationship between the number of ships and the amount of cargo that travels through the Panama Canal.