  Rotation curves are the key observational manifestation of the dark matter
distribution around late-type galaxies. In a halo model context, the precision
of constraints on halo parameters is a complex function of the properties of
the measurements as well as properties of the galaxy itself. Forthcoming
surveys will resolve rotation curves to varying degrees of precision, or
measure their integrated effect in the HI linewidth. To ascertain the relative
significance of the relevant quantities for constraining halo properties, we
study the information on halo mass and concentration as quantified by the
Kullback-Leibler divergence of the kinematics-informed posterior from the
uninformative prior. We calculate this divergence as a function of the
different types of spectroscopic observation, properties of the measurement,
galaxy properties and auxiliary observational data on the baryonic components.
Using the SPARC sample, we find that fits to the full rotation curve exhibit a
large variation in information gain between galaxies, ranging from ~1 to ~11
bits. The variation is predominantly caused by the vast differences in the
number of data points and the size of velocity uncertainties between the SPARC
galaxies. We also study the relative importance of the minimum HI surface
density probed and the size of velocity uncertainties on the constraining power
on the inner halo slope, finding the latter to be significantly more important.
We spell out the implications of these results for optimising the strategy of
galaxy surveys aiming to constrain galaxies' dark matter distributions,
highlighting spectroscopic precision as the most important factor.
