Important closed periodic orbits in an analytic rotating bar potential. The bar major axis is horizontal. Orbits elongated parallel to the major axis are members of the x₁ family. Orbits elongated perpendicular to the major axis form the x₂ and x₃ families. Superimposed on the orbits, we show a sketch of the equidistant anti-parallel vectors along which the stellar populations are binned and averaged. The cuts are numbered from 0 to 3, where #0 is crossing the centre of the galaxy and #3 is at the end of the bar. These numbers are found in the following figures and text.