Vampire-to-Human population ratios are roughly 1:5000. Downtown Chicago has a little under 3 million residents, and the vampire population is currently somewhere between 500 and 600 (the PC vampire population is about 1/20th of the entire PC and NPC population). The total count for Master Vampires is around 60-70.
Master Vampires are old, powerful vampires that have incredible supernatural abilities. Some can call animals to protect them, others can feed off of heightened emotion, some can decompose and recompose their bodies at will, some can fly, some can cause damage from afar, some can establish a power bond between themselves and a 'human servant', and others have unique powers they have worked on over the centuries that equally surpass those normal vampires. All of them are forces to be reckoned with who can 'bring over' humans and create new vampires far more successfully than non-master vampires can. If an attempt to bring someone over fails and doesn't just make a corpse, the human will return to the living as a revenant vampire. The revenant thinks of nothing but violence. Nothing can slow them down, not even holy objects backed by faith (unless destroyed by them). Masters are usually quite careful in that they very rarely create a revenant, and certainly not by choice.
Oftentimes, if a vampire hasn't exhibited any "master-like" traits in the first century or two of unlife, they most likely never shall. Generally, this involves them picking up some preternatural ability that isn't normally in the range of their bloodline. As far as estimations can tell, master-like traits tend to appear in about 10%-15% of the vampire population. For the most part, that's about the only difference between master vampires and "normal" vampires (if one will forgive the contradiction in terms) — although many of the master vampires like to claim that they are the natural leaders and the primary force behind the vampire population (as is evidenced by them calling themselves "Master" vampires) and that without them, there could never be any new vampires nor any civilized vampires, this is largely a propagandist smear-campaign intended to keep the standard vampire from running amok and giving vampires a bad name.
As such, many preterologists theorize that "master" vampires might be comparable to a genetic accident, like being born albino or with more than five fingers per hand, and are thus deviations from the standard "true" vampire template. Obviously, due to the self-claimed status, influence, and ego of many master vampires, such theories are not widely discussed. Interestingly, master vampires have only been found in the bloodlines that occupy positions in the Parisian Court, under the Mother of All Darkness.
"A vampire's only wish is to forsake all vampires" - Being Human (US) S.2 E.1
Master of the City (AKA: MotC)
There is a vampire in most major cities of the world that is known as the Master of the City. This vampire is in charge of the other vampires in the city or region, not unlike the leader of a pack of lycanthropes. Other vampires within the area must report to the MotC or risk being killed outright, in order to maintain the peace (So a wandering upstart vampire won't make the MotC of that area look bad). The Master of the City usually has other vampire officers that obey him/her directly, often biding their time in a political fashion. You see, traditionally the only way to become Master of the City is to kill the current MotC. Even if a non-master vampire kills the MotC, they have the rights to the office (although it'd be sitting on a very shaky throne). It is generally accepted that if a non-vampire kills the MotC, whoever kills the MotC's killer gets first claim. If the MotC vanishes or is killed with no known killer, the office goes to whoever first claims it as their own.
Also much like the leader of a pack of lycanthropes, it is entirely up to the current MotC to decide what practices are allowed or are not allowed. The one law is that whatever the MotC says is law, is law (up until the MotC is killed for their dumb laws).
A history of Chicago's MotCs can be found here.
Generally, the MotC can support a vampire population whose total Power is no more than 20 times his or her own Power.