percent in the Pew Research Center Typology Survey, and 13 percent in the American National Election Studies.
The antonyms for authoritarian is democratic or liberal and there are far more liberals and progressives than libertarians.
Rightardia suggests the lower left quadrants should be labeled liberal and the lower right libertarian. Liberalism is not a philosophy of the left, it is centrist. In the US most libertarians are on the extreme right. These changes would work in he US, but perhaps not in other countries.
It would also be useful to break up the X and Y axis in thirds: on the X-axis, authoritarian, centrist and democratic,. Likewise on the Y-axis, left. center and right.
The Political Compass model is flawed and has a libertrain bias. It confuses liberalism with libertarianism.