Why map galaxy structures?

The "cosmic web", as astronomers like to call the amazing 3D pattern of clusters, filaments and voids that they find galaxies to lie in, has been evolving -- shifting in shape and appearance -- since very soon after the Big Bang; the Universe has not always looked the way it does now. Early theories of galaxy formation, originating in the 1960s, supposed that many galaxies formed all their stars a very long time ago and that little activity had happened to those galaxies over the intervening billions of years since. More modern theories, including the "Cold Dark Matter" (CDM) theory, suppose that many galaxies have formed their stars much more gradually. We now believe that some combination of early and late star formation has ocurred, and that the rate of star formation within galaxies has depended strongly on the location of the galaxy within the continually-evolving cosmic web. Specifically, that some galaxies in very dense regions formed their stars rapidly, and hence a long time ago, and most galaxies in less dense regions continued to form stars much longer. To fully understand these processes, we must therefore map galaxies of all kinds across all the different environments within the vast cosmic web, and throughout the ages of the Universe.