Tree map is essentially a word cloud of all monitored paths in your organization. Each path is represented by a color-coded box. Mouse over a rectangle to display the path configuration; click once to reveal side panels; click twice to go to its path performance page.

Size by importance
Paths set to 1 will be bigger than those set to 5. Likewise, when you size by number of violations, and path with more violations will be bigger. Tree map does not display paths with zero violations during the selected period.
Group by path attribute
Paths will be separated and then sized; grey headers show attribute values.