Often, you'll need to use more than one axis to compare different measures, understand correlation, or analyze the same measure at different levels of detail. In these cases, you'll use the visualizations with more than one axis.
A scatterplot is an essential visualization type for understanding the relationship between two measures. Consider a scatterplot when you find yourself asking questions such as:
Does how much I spend on marketing really make a difference to sales?
How much does power consumption go up with each degree of heating/cooling?
Is there any correlation between hours of study and test performance?
Each of these questions seeks to understand the correlation (if any) between two measures. Scatterplots are great for seeing these relationships and also for locating outliers.
Consider the following scatterplot that looks at the relationship between the measures: the sum of Sales (on the X axis) and the sum of Profit...
