These graphs only plot calls made by the home plate umpire. In other words, they only plot balls and called strikes. No other pitches or results are included. Intuitively, this provides a representation of the strikezone for each game.
Each pitch is represented by a single dot. Green dots are balls and red dots are strikes. Pitches marked as belonging to a particular team (for example "bos" or "nya") are designated with different shapes. These teams represent the pitching team, not the batting team. So, a pitch marked "bos-Called Strike" was thrown by a Boston pitcher.
These are from the Umpire's perspective, not the Pitcher's perspective.
These strikezone maps are now drawn to reflect the 2015 zone "as called" to LHH and RHH hitters. These strikezone maps were drawn to the specifications of Mike Fast, a former writer for Baseball Prospectus who now works for the Houston Astros. These plots show actual calls superimposed onto dashed lines that represent the strikezones that all Umpires generally call. The dashed lines shift to represent typical deviations for LHH and RHH.