"axis equal" will set the aspect ratio equal between both axes.
"xlim" and "ylim" will set the axis limits which you can use to add margins.
axis equal % to set equal aspect ratio
ylim([-5,40]) % to add space above and below your data
xlim([-10,110]) % to add space to the left and right of your data
If you have the handle to you axis, it's best to specify the handle,
axh = gca(); % Get handle to axis
axis(axh,'equal')
ylim(axh,[-5,40])
xlim(axh,[-10,110])
