NGC 2403 H I channel maps of the data cube with both new and archival observations where we show only every second channel. The colour-scale contours correspond to 2 × (1, 4, 16, 64) × 10¹⁸ cm⁻², where 2 × 10¹⁸ cm⁻² is the 3σ one-channel column density limit. The thick contour levels indicate the significant emission identified by the SoFiA source finder. Most of the low-level structures shown in thin contours are noise or mosaicking artefacts. The dashed grey contours denote the column density of −2 × 10¹⁸ cm⁻². The egg-shaped borders are due to the 20% cut-off threshold of the primary beam response. At the bottom, we report the line-of-sight velocity (with respect to the systemic velocity 133.2 km s⁻¹) in each channel. The filamentary detections, labelled with coloured arrows, are evident between −59 km s⁻¹ and 47 km s⁻¹.