Heat Maps

A heat map is a 2-d version of the histogram that can be used as an alternative to a scatterplot. Like a scatterplot, the values of the two numeric variables to be plotted are placed on the plot axes. Similar to a histogram, the plotting area is divided into a grid and the number of points in each grid rectangle is added up. Since there won't be room for bar heights, counts are indicated instead by grid cell color. A heat map can be implemented with Matplotlib's hist2d() function.

Heat maps are useful in the following cases:

1. To represent a plot for discrete vs. another discrete variable

2. As an alternative to transparency when the data points are enormous