A Treemap displays hierarchical data as a set of nested rectangles. Each group is represented by a rectangle, which area is proportional to its value. Using color schemes, it is possible to represent several dimensions: groups, subgroups etc. Treemaps have the advantage to make efficient use of space, what makes them useful to represent a big amount of data. If you have many levels of hierarchy (>2), it is advised to build an interactive figure: clicking on a upper level of organization will reveal the next level and so on.