Comment by noctilux

Agree. I was confused by this at first but if the slope on lines without dividing by population is:

(log y2 - log y1) / (x2 - x1)

Then if we scale y2 and y1 both by c, which is 1 / population:

(log( c * y2 ) - log( c * y1 )) / (x2 - x1) =

(log c + log y2 - log c - log y1) / (x2 - x1) =

(log y2 - log y1) / (x2 - x1)

So scaling by population does not change the slope of the graphs, only the intercept.