A heat map (or heatmap) is a graphical representation of data where the individual values contained in a matrix are represented as colors. The term 'heat map' was originally coined and trademarked by software designer Cormac Kinney in 1991, to describe a 2D display depicting financial market information, though similar plots such as shading matrices have existed for over a century. - Wikipedia
Heatmap is a great way to visualize data and get insights on which area are most concentrated area of locations or values. It helps to make location decisions on new stores, new transport hubs, new distribution centers, new offices, shopping malls, etc.
It is visual and direct, easy to understand by everyone. Heatmap is a great tool for getting concesus and helps to convince the audience.
Geolytics is a great tool to create location based heatmaps. Below are some screenshots of heatmaps created by Geolytics.