I'm Scottish and I have never ever considered myself "northern". I'm Scottish, thanks. Yes, it might be the northern half of Britain, but I'd say we can be very different culturally. I remember traveling down to the north of England and passing the Angel of the North and laughing because it's essentially in the middle of the bloody country. Personally, I think that says a lot in terms of answering your question.
So, while it may be geographically correct to call us northerners, I suspect most of us would just prefer to be referred to as Scottish.