[Retric]

Norway only has a population density of 39 people per square mile which makes a huge difference. For comparison the UK is at 650 people per square mile. So 3% of Norway ~= 50% of UK in terms of people per square mile of farm land.

The real issue is food production costs are higher becasue of high labor costs, and poor weather / a relatively short growing season.

[Dewie3]

The ratio of "livable land" is also lower. Crops and humans seem to have that thing in common, not wanting to live at high altitudes or at the bottom of fjords. Though of course livestock don't mind grazing at higher altitudes, in the summer. And maybe having to have smaller farms leads to less efficiency of each "unit" of farmable land?

On the other hand, Japan is pretty mountainous and still has a high population density.

Norway probably didn't have that high population density 1000 years ago, either. But it was enough to cause overpopulation, and in turn motivate the events and practices of the Viking Age.