Learn in the textbookBasic Charts and Visualizing Distributions
DefinitionA heatmap (ヒートマップ) shows the size of numbers arranged in a table or similar grid as shades of color or hues.
ExplanationWith days of the week as rows and time slots as columns, for example, cells with more visitors are painted darker, so the busy time slots stand out as patches of color. Without reading each number, you can grasp at once where the high and low values lie.
AnalogyOn a thermal camera screen, the warmer parts of a body glow redder, so you can spot the hot areas without reading any numbers.
Memory hookHeat: the hotter (larger) a value, the darker or warmer the color it gets.