Professional Boxing has four major sanctioning bodies namely, WBC,WBA,IBF,WBO. Because of this division in sanctioning bodies, the sport does not have a centralized ranking system.
The rankings are published in a way that no two bodies have the same champion. This is done so that each body's champion is always available to frequently defend the championship against its top-ranked contender.
There is often more than one champion for the WBA and these champions are not present in the rankings of any of the other three bodies. The 'Super' and 'Regular' champions of the WBA are excluded from the rankings but their #1 spot is secured for the 'Interim' champion.
The top two places of the IBF's list are kept vacant until two of its other top-ranked contenders face off. The winner of this face-off fills in one of those vacant ranks.