Sketch of a rotating elongated bar in a face-on disc to illustrate the axes along which the stellar population gradients were measured. The solid-line elongated ellipse outlines the bar that rotates counter-clockwise as indicated by the arrow. The dashed lines mark the bar major and minor axes and the dot-dot-dashed circle gives the bar radius. The gradients discussed in Sect. 4.1 were measured along the blue arrows and the gradients in Sect. 4.2 along the green arrows. MA – along the major axis; MI – along the extension of the minor axis; L – from the major axis towards the leading edge of the bar; T – from the major axis towards the trailing edge of the bar.