Very large spatial scales – visibility plots: these plots show the observed (left) and reconstructed (right) visibility functions for a simulation in which a large extended flat-spectrum source is observed with an interferometer with a large central hole in its uv-coverage. The colours/shades in these plots represent 6 frequency channels spread between 1 and 4 GHz. The top row of plots shows that when no short-spacing information was used, these data can be mistakenly fit using a less-extended source with a steep spectrum. The bottom row shows that the inclusion of short-spacing information is sufficient to reconstruct the sky brightness distribution correctly.