Development of heat maps dated back to the 19th century to provide a graphical representation of complex data so that it is easier for humans to analyze at-a-glance. Back then, a gray-scale shading was used to depict data patterns and the darker color was used to indicated dense values while lighter color was used to depict lesser values. A few applications of heat maps include depicting weather reports, real estate market data, and financial market analysis. The beauty of using heat maps is that you don't have to read a table of data in rows and columns to understand complex data, but rather view a simple colored map to grasp the big picture of data representation.