Flags flying at half-mast

For couple of these weeks, most flags in Vancouver were flying at half-mast. I didn't know the reason and my friend told me that they were the expression of condolence to the terrible affair happened in London. It was an unexpected answer for me because In my daily life I rarely mind the relationship between England and Canada. The relationship with U.S. seem to be greater whether Canadian people like it or not. So, I'm interested where the flags were flying when the 9.11 shocked the world. Today the flags got back to the ordinary position and time flies day by day like this.