Simultaneous mapping of chemical abundances and magnetic field structure in Ap stars

Magnetic A stars represent about $5\%$ of the upper main sequence stars and exhibit highly ordered, very stable and often very strong magnetic fields. They frequently show both, brightness- and spectral line profile variations synchronised to stellar rotation, which are believed to be produced by atomic diffusion operating in the stars' atmospheres, that are stabilized by multi-kG magnetic fields. In recent years, with the development and the application of the Doppler- and magnetic Doppler imaging technique and the availability of high precision spectroscopic and spectropolarimetric data, it has became possible to map chemical abundances and magnetic field structures of Ap stars simultaneously and in more and more detail, based on full Stokes vector observations. Here I will review the state-of-the-art in understanding Ap star spots and their relation to magnetic fields, the development of Doppler- and magnetic Doppler imaging into one of the most powerful astrophysical remote sensing methods and the physics of Ap stars atmospheres we can deduce from the simultaneous mapping of magnetic field structure and chemical abundances.