As you explore and analyze data, you'll often want to understand how various parts add up to a whole. For example, you'll ask questions such as the following:

• How much does each electric generation method (wind, solar, coal, and nuclear) contribute to the total amount of energy produced?
• What percentage of total profit is made in each state?
• How much space does each file, subdirectory, and directory occupy on my hard disk?

These types of questions are asking about the relationship between the part (production method, state, file/directory) and the whole (total energy, national sales, and hard disk). There are several types of visualizations and variations that can aid you in your analysis.