The x-axis lists the 92/93 - 13/14 seasons. The y-axis is the team's overall place in all 4 divisions (ie 1st in Championship is 21st). The middle lines show the mid-table position of each league.
The darker the shade, the lower the division it represents. The Premier League is the lightest, at the top. There are 92 teams in all four divisions. The first three seasons held 22 teams in the Premier League, hence the slight jump in boundaries.