  A better understanding of the formation of mass structures in the universe
can be obtained by determining the amount and distribution of dark and luminous
matter in spiral galaxies. To investigate such matters a sample of 12 galaxies,
most with accurate distances, has been composed of which the luminosities are
distributed regularly over a range spanning 2.5 orders of magnitude. Of the
observed high quality and extended rotation curves of these galaxies
decompositions have been made, for four different schemes, each with two free
parameters. For a "maximum disc fit" the rotation curves can be well matched,
yet a large range of mass-to-light ratios for the individual galaxies is
required. For the alternative gravitational theory of MOND the rotation curves
can be explained if the fundamental parameter associated with MOND is allowed
as a free parameter. Fixing that parameter leads to a disagreement between the
predicted and observed rotation curves for a few galaxies. When cosmologically
motivated NFW dark matter halos are assumed, the rotation curves for the least
massive galaxies can, by no means, be reproduced; cores are definitively
preferred over cusps. Finally, decompositions have been made for a pseudo
isothermal halo combined with a universal M/L ratio. For the latter, the light
of each galactic disc and bulge has been corrected for extinction and has been
scaled by the effect of stellar population. This scheme can successfully
explain the observed rotations and leads to sub maximum disc mass
contributions. Properties of the resulting dark matter halos are described and
a ratio between dark and baryonic mass of approximately 9 for the least, and of
approximately 5, for the most luminous galaxies has been determined, at the
outermost measured rotation.
