DW-Nominate is obviously more statistically sound than Political-Compass, But they are not measuring the same thing.

DW-Nominate is a tool based on congressional votes in the US, and in Clinton’s case these votes were entirely during the Bush II era. The vast majority of bills that were voted on during that time were right-wing or at most center-right bills. So, yes she was the 11th most liberal Senator during that time, that still doesn’t actually make her progressive. It just makes her more progressive than most of her colleagues at the time.

Political Compass tries to take a much much wider view of the political spectrum, and plot all the world’s practical and theoretical systems on the same scale. So on it most US politicians will end up in the upper right quadrant and look very close to each other, because they are all capitalists. One should imagine the exact center as being post-WWI German Social Democracy or FDR New Deal style politicians. This leaves the entire left wing of their graph for actual Socialism.

More than likely their exact placements of candidates aren’t statistically rigorous, but the neighborhoods are very likely accurate.