Median rms map of all 391 pointings as a function of σ₂₀, showing increased noise in the pointing centre and towards the edges of the image. The contour lines show the levels (1, 2, 4) × σ₂₀ in the image. For the pointing with the lowest <τ₂₀, J2339-5523, the range l-5σ₂₀ corresponds to 12–60 µJy beam⁻¹. For the pointing with the highest σ₂₀, J1244-0446, the range l–5σ₂₀ corresponds to 0.4–2 mJy beam⁻¹.