Redshift space is a concept of cosmological space based on spherical coordinates (with us at the center), taking the redshift of objects (galaxies and other distant bodies) as found in redshift surveys as the radial dimension. A collection of data over three dimensions, such as throughout some redshift space, is termed a data cube. Mapping redshift space by means of such surveys is used to determine geometry of the universe over time, e.g., the accelerating expansion, or dark energy.
Hubble's law gives a means of converting between redshift space and "normal" space, but can yield errors due to redshift space distortion or RSD, the effect of the peculiar velocity of galaxies on their redshift, e.g., in an region where galaxies have high random peculiar velocities (appearing stretched toward and away from us, i.e., the finger of God distortion) or a pattern of high peculiar velocities (e.g., when they are attracted toward the center of a larger structure, the Kaiser distortion). The Alcock-Paczyński effect also presents complications. Data stored as redshift space can be thought of as the "raw data", as yet uninterpreted, allowing interpretation when needed, perhaps using methods developed and/or data collected in the mean time. However, much analysis can be carried out without converting from redshift space.