The why axis is labeled as a measure of "Intergenerational Earnings Elasticity". Based on that description, I would expect that higher numbers would correlated to higher elasticity. In other words, higher numbers would imply more ability to earn a different amount from what your parents earned. It looks backwards.

I also question how accurate it is. Denmark's earnings elasticity is near the very bottom of the scale. It appears that the scale is not 0 based (which implies someone was trying to goose the slope of the line), but it still puts Denmark very, very low. I don't know much about Denmark or the other Nordic countries, but I do have a lot of experience working with Canadians. They are below 0.2 on the scale. Again, I don't understand the exact measure being used here, but the implication is that what a Canadian earns has very little relationship to what their parent's earn. I don't doubt that their mobility is greater than it is in the US, but it isn't that strong. The majoriy of Canadians I know (admittedly not that large of a sample) are in roughly the same earnings group as their parents.

The data is from Miles Korack's research.

The y axis is an expression of the percentage difference among a population's incomes and their parent's incomes. A "1" at the top of the scale is a 100% match to the parents' incomes. A ".5" is a 50% match, i.e. if your dad made twice what my dad made, then you would be making 50% more than I make.