As sega_sai said, there are patterns in the way the galaxies are distributed. Around every galaxy, there is a ring where there is a greater chance of finding another galaxy. It's called the Baryon Acoustic Oscillation, and measuring it is the reason we took these images in the first place! Measuring the size of that ring at different times in the past will hopefully help us figure out how dark energy behaves. See desi.lbl.gov, eg.