A heat map is a representation of data using colors in two dimensions. A heat map uses warm to cold color spectrum in which the warm areas' values are high and the cold areas' values are low. There are many ways to display a Heat Map but they all use color to represent the data.
In order to understand how visitors behave on your website, heat mapping is crucial. Every mouse move, click, keystroke determines the heat map of a web page.
Reading a heat map depends on which data is representing in that particular map. Bear in mind that, warmer colors indicate higher values and colder colors indicate lower values. Red is the warmest color and purple is the coldest one in these maps.
You need to analyze colors and understand the intensity of the map. For example, in the image above, the intensity is the highest at the first 5 searches. This map shows us that the top 4-5 pages in a Google search get the attention majorly. Also, the shopping part of the page is red because of the visual source.
There are many websites that you can use to generate a heat map. Although there are numerous ways to analyze data, a heat map provides you a visual and clear representation. It is useful for looking at your web page from a browser's perspective and customizing and replacing things in warmer and colder areas.