A tree map visualizes a tree as nested rectangles.

Representing a Tree

A tree is a recursive data structure. In a language like Haskell, we would model a tree as an algebraic data type:

data Tree a = Leaf a | Branch [Tree a]

A tree is either a leaf or a branch, where a leaf contains some information, and a branch contains a list of trees.

In Python, we can model this using a dataclasses:

An Example Tree

Given the three types (Tree, Branch, and Leaf), let's construct an example tree.

Computing over the tree

Let's write a function to sum up the values of a given tree. For this we use Python's pattern matching feature (the match-case statement). If the tree is a leaf, we return the value of that leaf. If the tree is a branch, we sum up the totals of all subtrees.

Now let's compute the total over our example tree:

Visualizing Trees with Tree Maps

Now we are ready to develop our tree map visualization.