The Silver Slugger Awards are always a bit weird. The awards, voted on by coaches and managers across the league, are meant to recognize the top offensive performers at each position in both the American League and National League.
One caveat here is that outfielders are not divided up by position...they are all lumped together by the voters and the top three get the award. This makes a certain amount of sense although it does stink that a centerfielder is highly unlikely to win the award given this arrangement. The awards can also get really weird when it comes to guys that play multiple positions like Javier Baez, for example.