How do you define Northern/Southern CA?

[Max Rockatansky]

If dividing the state into two halves, yes, 198 is about right.

One could also make the case for more regions - north coast, valley, east of the Sierra, SE... but that gets more complicated.

I'd say the boundary point of the Sierras at the Tehachapi Range CA 58 is much more of a true indicator of what is "north" in California.  I don't think anyone would really consider any part of the Sierras as something associated with "Southern California."  Interestingly I think that Bakersfield would be considered part of the Southern Part of the state by most but certainly not Fresno lending credence to 198 being the line.