To introduce the topic of this chapter, let me first show you a visual display that will help you realize the significance of profiling: a chart with a lot of data points that could benefit from a structure to process a large amount of data. The graphical table in Figure 13.1 represents the estimated percentage of people in each single-year age group (0 to 100 years old and more) in each of the 3,141 U.S. counties. Row height encodes population size for that county. Counties were sorted by median age. Higher proportions are encoded in red, while lower proportions are encoded in gray.