Astrometric errors caused by a GW with P_gw = 20 yr (ν ≃ 1.58 nHz) propagating towards the centre of the maps with strain parameters $h_{+}^{\text{c}}=h_{+}^{\text{s}}=h_{\times }^{\text{c}}=h_{\times }^{\text{s}}$. In the legend, ε is a placeholder for any of the five astrometric parameters. The maps show the median error, normalised by ∆_max, using a pixel size of ≃0.84 deg² (HEALPix level 6). The projection is the same as in Fig. 1. The black curve marks the ecliptic.