Neighborhood/City security ratings, A question about security ratings and changes since published last Options

[Gerdofal]

Okay, so Runner's Companion just came out... and it mentions the same kind of security rating system as before (ex. "an area with security rating of B" on p 22). Unfortunately, these security ratings have never been explained or listed in any SR4 material. (That is, unless I missed it somewhere.)

The term is not even used in Runner Havens or the core rulebook, nor is it mentioned anywhere else in Runner's Companion. In fact, the last time I think it was published was in SR3 somewhere.

Was this an oversight then? Or did I miss an obvious list somewhere?

And, that being said, what I really want to know is have they changed any since SR3? This is especially applicable to Hong Kong, which could have seen considerable changes.

Thanks!