By default, graphs display in a rectangular axes that has the same aspect ratio as the figure window. This makes optimum use of space available for plotting. You exercise control over the aspect ratio with the axis function.
t = 0:pi/20:2*pi; plot(sin(t),2*cos(t)) grid on
produces a graph with the default aspect ratio (the same as axis normal).
axis square — makes the current axes region square
axis equal — sets the aspect ratio so that the data units are the same in every direction
axis equal tight — sets the aspect ratio so that the data units are the same in every direction and then sets the axis limits to the minimum and maximum values of the data.