It's hard to compare the events and the psychological impact, but keep in mind that most of the victims are children, came from all over the country and knew the PM and rest of the parliament, especially the Labour party.

As far as I know, September 11 was an attack that killed people who worked in office and affected people who lived in or near New York the most, and did not hurt Bush administration like the Oslo-attack did.

I would suspect that may make it worse to bear for the Norwegian people, but as stated, it's hard to compare.

The September 11 attacks also struck the Pentagon in Washington, DC, which would have the same effect on members of the American administration.

Did anyone die in those attacks? Didn't the plane hit a segment of the Pentagon which was under construction and unoccupied?

Yes, 125 people died at the Pentagon: http://en.wikipedia.org/wiki/September_11_attacks#Casualties

Ah I see, that area of the Pentagon was under renovation but not entirely unoccupied at the time of the attacks. (http://en.wikipedia.org/wiki/The_Pentagon#September_11_attac...).

There is a memorial for those who died on the Pentagon's western boundary http://www.whs.mil/memorial/

Another fact to contrast the magnitude is the fact than in 2009 there was a total of 31 homicides in Norway. This attack produced more than two years of homicide victims.

http://www.ssb.no/english/subjects/00/minifakta_en/en/main_0...

Wow. That's incredible. In Montana we have just shy of 1 million people. According to the stats there were 28 murders in 2009. Montana is a very safe state and that's still 5 times Norway's murder rate.

why try to quantify the unquantifiable?

Human nature.