Even for slow rotators it will be possible to construct longitudinal maps using the combination of optical and UV light curves provided by STARS. Ground-based photometry, monitoring variability with amplitudes from 0.5 mag down to 0.05 mag, indicates that large spotted areas covering up to 40-50% of the stellar surface exist in the most active systems (e.g. Strassmeier and Bopp 1992). In contrast, solar-sized spots are expected in less active, slow rotators, producing modulations of only 10-100 ppm at visible wavelengths. Since spot formation and decay are slow processes, STARS will achieve the necessary photometric precision (about 1 ppm on a time scale of one rotation period) and time baseline necessary to detect and map such small features for the first time. Magnetic plages have the advantage that they are bright in the UV and much larger than spots, while there is also a strong contrast between quiet and active regions. For slow rotators, light-curve imaging in optically thin UV lines is an attractive technique for STARS yielding information on (longitudinal) plage structure and (differential) rotation.