Left: positional offsets of selected cross-matched sources between two catalogues, one is extracted from the 6′′ resolution LOFAR deep image of the ELAIS-N1 field, and the other one is obtained from our current image at a resolution of 1.2′′. The median values of the offset are dRA = −0.0047′′ (σ = 0.0623″) and dDEC = 1.1864′′ (σ = 0.0336″). Right: positional offsets of selected cross-matched sources from two catalogues, one is the optical catalogue of the ELAIS-N1 field, and the other one is our corrected radio catalogue. The median values of the offset are dRA = 0.0083′′ (σ = 0.0817″) and dDEC = −0.0762′′ (σ = 0.0605″). The near-to-zero median values validate the quality of the position offset correction. The error bar of each source is taken from the source extraction output of package PyBDSF.