VISTA RGB composite with Y (1.02 μm) in blue, J (1.25 μm) in green, and K_s (2.15 μm) in red showing the north-eastern corner of the pilot field. Green crosses are placed at the centres of the grid elements (90″ radius in this instance). The small yellow circle highlights an example grid element, while the large white circle shows the area searched to identify suitable control field regions (see text).