What are the differences between curves and levels in terms of data analysis and visualization techniques?

Curves and levels are both tools used in data analysis and visualization, but they serve different purposes. Curves are used to show the relationship between two variables, typically by plotting one variable against the other on a graph. Levels, on the other hand, are used to represent the magnitude or intensity of a single variable across different categories or groups. In essence, curves show the relationship between variables, while levels show the distribution or variation of a single variable.