Well, the general consensus in the past has been... Well, not much of a consensus. There's some clear points (a general 1% of the world population is Awakened, with variable counts in a number of regions to either direction (Aztechnology/Aztlan has an average of 2% Awakened, for example). Your example of 9 Aspected Magicians for every normal Magician is actually accurate as of... Street Grimoire, I believe.
The main issue is where the books explain that only a 'fraction' of the 1% are actually functional. A lot of the Awakened end up being:
A. Unaware of their Awakened status; the talent needs to be found and nurtured, and they got missed.
B. Burned out, whether it be from drugs, 'ware, Essence drain or something else.
C. Ineffective. A number of the Awakened aren't really mana-slingers, they're just sensitive to the presence of magic or things going on. There aren't really any by-the-book mechanical means to represent this at the moment. Maybe they tried and couldn't cut it, maybe they just never bothered.
D. Insane. Magic does weird things to your head, and a lot of people who try to learn it can get all sorts of messed up. This is also where Toxics, Bug Shamans and Blood Mages fall.
These factors can make them the equivalent to a magical non-entity.
So, how big is this fraction of functional Awakened compared to the dross? Most people tend to make it less than 50%, because why call it a fraction when it's a majority? After some discussion, I (and a few others) went with a flat 25% of the Awakened population is functional; i.e. they have an appreciable Magic Rating and skill. This is anywhere from the Magic 1, newly Awakened street-punk who can light cigarettes with the snap of his fingers to Harlequin-level, dozens-of-initiations super-magicians.
The other 'problem' is they never give a clear proportion of adepts to magicians. Sure, there's 9 Aspected Magicians to every Magician, but how many Adepts to the spell-slingers and summoners? I pulled 20% out of my ass, mostly because nothing suggests they're more common than magicians, but not extremely rare either.
So, the numbers I and a few others use, out of one million:
1,000,000 People.
Now, 1% of 1,000,000 is the 'Awakened' Metahuman population.
-990,000 Mundanes.
10,000 'Awakened.
The functional fraction we're using is going to be 25%.
-7,500 Crazies, Incompetents, Untapped Talents, Burn-Outs.
2,500 Functional Awakened.
This is where we break it down into the kinds.
1,800 Aspected Magicians
~600 Conjurers
~600 Sorcerers
~600 Enchanters
200 Full Magicians
500 Adepts
Now, I don't give a slot for Mystic Adepts. I generally figure they're much rarer, and they'd mess up my pretty, even numbers. So I just hand-wave that they pop up occasionally in the Full Magician or Adept pool once in a while.