The heat maps available in FanGraphs PITCHF/x section represent where a pitcher threw a particular type of pitch the most often.
There are some other important things to note:
● All pitch type classification is based on MLBAM’s pitchf/x pitch types. The algorithms used over the years are not always consistent, so be careful when comparing pitch types between years.
FA - Fastball CU - Curveball FT - Two-seam Fastball CH - Changeup FC - Cutter SL - Slider FS - Splitter KN - Knuckleball PO - Pitchout IN - Intentional Ball AB - Automatic Ball UN - Unknown Pitch
● The heat maps are generated by creating a scatter plot of the pitches and then applying color of varying degrees to overlapping points. The more points that intersect, the greater the intensity of the color.
● You can change the size of each point in the scatter plot. Making the points larger will having a smoothing effect on the heatmap. You can also change the intensity, which will make the colors more intense for each point that is plotted.
Much of the code used to create the heat maps was found on Dylan Vester’s C# Playground.
Links for Further Reading:
David Appelman is the creator of FanGraphs.