Left and right is economic. The further left, the more you want shared or public ownership and a narrow gap between rich and poor. The further right, the more you trust private property, markets and the inequality that comes with them.
Up and down is about the state's power over people. At the top, order, surveillance and firm leadership are worth some loss of liberty. At the bottom, privacy and personal choice come first, up to the point of wanting no state at all.
Both lines run from −10 to +10. On this site they come from two of the twelve axes of the 12 Axes test, Economy and Power, and a score inside the Balanced band (40 to 60) counts as centre. That gives four quadrants, four centre lines and a centre square. The shaded cross on the chart marks that band.