Galactic properties are investigated in a wide range of environments by three dimensional imaging in the neutral hydrogen line. The main topics addressed are large scale structure and galaxy evolution. A survey of carefully selected areas with different galaxian densities is made, searching for gas rich systems. This settles the question as to whether gas rich dwarf galaxies are more uniformly distributed than luminous galaxies, a question long unanswered. In addition, a complete survey of the Hydra Cluster of galaxies is made. This is the first time that a volume limited HI survey of a cluster of galaxies has been carried out. These data are complementary to the wealth of already available single dish data on the global HI properties of galaxies in clusters. A detailed study is made of the effects of the environment on the evolution of galaxies. Details of the gas removal mechanisms at work, which are known to deplete the atomic gas in the galaxies, are studied with particular attention to the possibility that enhanced star formation occurs due to compression of the gas by the intergalactic medium. From the two-dimensional velocity fields of the gas the mass distribution of the galaxies is derived and compared with that of galaxies in the field, thus establishing whether dark matter is associated with galaxies in clusters in a similar way to those in the field.
