In cartography there has been almost a revival of heat maps in recent years. I should start by clarifying what I refer to by the term ‘heat map’.
Across different disciplines, heat maps mean different things from isotherms in meteorology to pixel matrix displays in graphics and computing. In cartography and GIS, the term is used to represent location weighting or densities. Caitlin Dempsey gives a very good description on GIS Lounge:
‘Heat mapping, from a geographic perspective, is a method of showing the geographic clustering of a phenomenon. Also known as hot spot mapping, heat maps show locations of higher densities of geographic entities.’