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Tree Map - What is it ?

Objectif : Visualize hierarchies or complex structures.

A Treemap, also known as a box map or proportional map, is a data visualization technique. It allows you to visualize hierarchical information in a tree-like diagram. The data is organized into branches and sub-branches.

The difference with the tree diagram is that a treemap also shows the quantity associated with each category. Indeed, each category is represented by a rectangle whose size represents the corresponding quantity.

Here is a schematic example:

Treemap example

Moreover, the color of the boxes can also represent a second value. It is therefore possible to present two quantities per category. Each of the rectangles also contains smaller rectangles representing the sub-categories.

Treemaps were originally invented by Ben Schneiderman. His goal was to view a folder of files on a computer without taking up too much space on the screen.

Indeed, this diagram is ideal for displaying hierarchies since it presents information in a compact and space-saving way. It also allows you to see a structure at a glance.

If you need to view a very large amount of hierarchical data, this is the right choice of diagram.. It is possible to present several tens of thousands of data points on such a graph.

The Treemap is also suitable for studying data with two quantitative values, since it is possible to indicate one value by the size of the boxes and another by their color.

A box map is also suitable for comparing several categories, since the quantities are proportional to the size of the boxes. Similarities and anomalies between categories can be identified very quickly. Trends and patterns also stand out explicitly.

Finally, these diagrams make it possible to organize the data at several levels. It will be very easy for the user to "zoom in" on a category to study the data at different granular levels.

However, the main drawback of a Treemap is that it does not present the hierarchical levels as clearly as other diagrams entirely designed for dataviz of hierarchical data. Examples are the tree diagram or the sunray diagram.

It is also not possible with a treemap to represent data of varying magnitude. Data corresponding to the size of a rectangle cannot have a negative value either.

Similarly, although the representation of values by the size of rectangles is intuitively readable, the task is still more complex than on a diagram whose values are indicated by the length of a line or bar..