Radial and height cross sections of our spiral galaxy electron density model n_e,spiral (r, h) (pink lines). Constituent components of the model tracing the inner MW Galactic disc (Gómez et al. 2001; Schnitzeler 2012) (blue lines) and an ionised outer HI disc model (Kalberla & Dedes 2008) are shown (brown lines). Shaded (blue/brown) regions highlight areas in which the inner/outer profiles are considered well constrained. The horizontal black dotted line indicates the approximate electron density for the IGM at z_s = 0 (Ioka 2003).