The cube is just a notional device to balance three spectrums in your head at once.
Urban-Rural
Richer-Poorer
Whiter-Darker
Don’t fixate on exact salaries, distances, or populations. It is literally a device for relative comparison.
Yeah, well, I am an engineer, we like to quantify and measure things. Things do not work if you do not fixate, but I know what you are saying.