Slide 10
This map of Napoleon's march across Russia (so lauded by Tufte) allows for the simultaneous comparison of a number of variables (e.g. temperature, position, date, army size). What would allow for similar types of analysis of a program's source code or execution? Which variables would we want to compare? How should they be displayed to facilitate this comparison? Additionally, as Tufte discusses with his concept of 'small multiples', the simultaneous viewing of data collected at different time facilitates comparison; the snapshot approach used by debuggers made it difficult to perform this type of analysis.