Interstellar polarisation of the field stars around observed high-polarisation standards (Heiles 2000). High-polarisation standards are marked with a star symbol and are located at the centre of the images. The degree of polarisation is proportional to the length of the orange straight lines. The horizontal bar at the top left presents 4.0% polarisation. The colour of each star corresponds to its distance. The distance is based on Gaia Early Data Release 3 (Bailer-Jones et al. 2021). The background image represents 100 μm dust emission maps (Schlegel et al. 1998).