Strength of schedule is calculated from the opponents projected fantasy points allowed for the DB position. The best rating is +16 which gives the player the advantage against the defense and indicates an easy opponent, the worst rating is -16 which gives the defense the advantage and indicates a tough opponent.
Peterson is rapidly developing a reputation as one of the NFL's better young cornerbacks. However, that reputation hasn't really translated to IDP production, as despite seven interceptions last year Peterson still finished outside of the top 30 defensive backs in Fantasy Sharks Default IDP Scoring. The third-year pro is an OK starter if your league requires cornerbacks, but in my experience Paterson is overvalued in IDP drafts this year.