The Sloan Digital Sky Survey is two separate surveys in one. Galaxies are identified in 2-D images (right), then have their distance determined from their spectra to create a 2- billion-light-year-deep 3-D map (left) where each galaxy is shown as a single point. The color represents the galaxy's luminosity. This 3-D map shows only 66,976 out of 205,443 galaxies that lie near the plane of Earth's equator.
Sloan Digital Sky Survey