Heat Maps in Web are often used as web analytics instrument, showing the statistics of site pages attendance; they are quite common in biology and medicine as well. Generally, these charts might be used wherever we need to show the hierarchy of some values in some categories. They look as tables with cells colored differently in due to the significance of the value this cell represents.
This Chart shows us how the server fans work. There are ten servers with fifteen fans in each, and they all work different speed due to some reasons. There are three ranges of the Color Scale: low (under 1300), medium (1300-2300) and high (2300-3000); each point representing a fan of a server is colored with a color of a range it belongs to. Tooltips are disabled because they are unnecessary; stroke of the axes is turned off but the labels are on and both servers and fans are enumerated from zero. The legend is enabled; you can use it to select and highlight all points that belong to a range by clicking or hovering this range’s legend item. Also you can click the points itself to select them (hold the Shift or Ctrl key to select more than one point).