We present constraints on the space densities of both non-magnetic and
magnetic cataclysmic variables, and discuss some implications for models of the
evolution of CVs. The high predicted non-magnetic CV space density is only
consistent with observations if the majority of these systems are extremely
faint in X-rays. The data are consistent with the very simple model where
long-period IPs evolve into polars and account for the whole short-period polar
population. The fraction of WDs that are strongly magnetic is not significantly
higher for CV primaries than for isolated WDs. Finally, the space density of
IPs is sufficiently high to explain the bright, hard X-ray Galactic Centre
source population.Comment: Proceedings of the conferencs "The Golden Age of Cataclysmic
Variables and Related Objects II", Palermo, 9-14 September 2013. Accepted for
publication in Acta Polytechnica. 6 pages, 4 figure
