Up until the latter part of the 20th Century astronomers thought, in the words
of the eminent astronomer Edwin Hubble, that the universe was "sensibly uniform."
As a result of redshift surveys of large samples of galaxies we now know that
the galaxies around us are distributed in an incredible tapestry of filamentary
and sheet-like structures called the cosmic web. Massive clusters of galaxies
lie at major "intersections" in this web. Galaxies like our own Milky Way are
usually found in groups which often lie on the outskirts of clusters or
superclusters. The first really large structure, the
Great Wall, was discovered by CfA astronomers in the late 1980's and is
approximately 300 million light-years across.
CfA Redshift Survey
CfA Redshift Catalog
2MASS Redshift Survey
Updated Zwicky Catalog