Assume the dipole model for earths magnetic field $B$ which is given by the vertical component of magnetic field, $B_V=\frac{{\mu }_0}{4\mathrm{\pi }}\frac{2m \cos \theta }{r^3}$ and the horizontal component of magnetic field $B_H=\frac{{\mu }_0}{4\mathrm{\pi }}\frac{m \sin \theta }{r^3}$, where $\theta$ - latitude as measured from magnetic equator, then the loci of point for which dip angle is $\pm 45°$.