Tomography plots of the individual absorption spectra around the Na I doublet for a simulated hot Jupiter. The top panel shows the case without stellar activity, the middle panel includes the effect of a stellar spot with a coverage fraction of f_sp = 1%, and the bottom panel displays the isolated spot contribution, obtained as the difference between the two upper panels. The color scale represents the absorption (1 − F_in/F_out) in percent, while the dashed white line traces the expected planetary trail. The horizontal black lines indicate the four contact points of the transit. For this case we adopt v sin i = 2 km s⁻¹.