The galaxy M81 (NGC 3031) belongs to the Hubble class SA(s)ab. Its disk is inclined by 59° with respect to the sky plane. The galaxy has a distance median value of 3.6 Mpc. M81 is famous for its well-pronouced spiral arms in gas and total radio emission, which are thought to be the result of compression of gas and magnetic fields by density waves. In contrast, the polarized radio emission emerges mainly from the interarm space.