Rectangular Heat Map

Here's a snapshot of Rectangular Heat Maps from my recent project "Your guide to Data Visualization". Check out the complete project on Medium and Behance.

Heat map represents the variable under comparison for various categories as heat signatures. The hotter a certain category appears the higher is the value of the variable under comparison for the category. Heat maps allow easier and faster readability of the data in order to identify the extremes. There are various types of heat maps — Rectangular, Circular, Spiral, Geographical, etc. The most commonly used heat map is the rectangular one where the heat signatures are presented in a matrix. Have a look at the example to understand what I’m referring to. As you can see, if we were to replace the grids with the values of the variable, it would give you a table.

The rectangular heat map here demonstrates the traffic on a website via various channels over a period of 4 years. Looking at the heat map you can easily decipher which channel contributed how much to the traffic every year relatively. Now if you wish to showcase the absolute values too, you can put this on top of the heat map. This makes the heat map more useful to the user. Depending on the data and the use case, heat maps make use of either specific set of colors which will have defined range of values for each color, or it can make use of gradient colors in which case the entire gradient represents a range as shown in the example.

Best Practices for Heat Maps
1. Ensure a high contrast between the colors used to represent extremes of the heat signature or intensity (too cold and too hot, or high frequency and low frequency).