# Radial Treemaps: Extending Treemaps to Circular Mappings | by Nick Gerend | Dec, 2023

## The Treemap Concept

The “Treemap” was introduced by Ben Shneiderman at the University of Maryland in the early 1990s¹. Simply put, it’s an efficient way of displaying hierarchical data as a set of nested rectangles. Although the concept is simple, the arrangement of the rectangles is subject to an aesthetic preference, and various arrangement algorithms have been developed to enhance the appearance of the final layout.

## Treemap Mechanics

Given a hierarchy, a Treemap represents each branch in the hierarchy as a rectangle, which is then tiled with smaller rectangles representing sub-branches. The space in a Treemap is divided according to a specific attribute of the data (often size or value), and each rectangle’s area corresponds to the attribute’s magnitude, making it easy to compare different parts of the hierarchy.

To account for the arrangement of the rectangles, here are some of the common algorithms that govern a Treemap’s construction and ultimate appearance:

• Squarified Treemaps² – creates rectangles as close to squares as possible by adjusting the aspect ratio of the rectangles
• Strip Treemaps³ – lays out the rectangles in strips, either horizontally or vertically, based on the data’s hierarchy
• Slice-and-Dice⁴ – alternates between horizontal and vertical divisions which is straightforward but can create elongated rectangles

## Treemap Features

• Proportions – the size of each rectangle is proportional to the data point it represents, allowing quick identification of larger and smaller items
• Lines and Colors – clever usage of borders, border size and color, and buffers can delineate hierarchy levels while container colors are often used to represent different dimensions of the data
• Spatial Efficiency – Treemaps…

This post originally appeared on TechToday.