Note that the question was for source density, not pawn density, an entirely different thing.
Really? You think having 2 vis sources makes you rich beyond the wildest dreams of avarice? You are setting the bar way too low. Or did you mean in the high fantasy setting (which is called high fantasy for a reason)?
And I designed a covenant by Lake Balaton with 29 sources over 3 sqm and an annual take of 94 pawns. What's your point?
Well, my point is: IĀ“d like to know what happened.
I have two Ars Magica Sagas. The first is a more or less vis-poor saga, but the covenant has a very good library. Vis is not very important in this saga.
In the second saga, I wanted to have a different approach. The players have a starting spring covenant with nearly no books. My intention is to be avaricious with books. To compensate I want to offer the covenant more vis sources, but "an annual take of 94 pawns" is much more than I imagined. So tell me what happened, what did the players do with this vis? Maybe I can learn something for my second saga.
Chiarina
The forums have become everything that the Berklist ever was....
Too new for familiarity with Berklist, is this forum being like that a positive or negative thing?
As far as I know the Berklist was notorious for heavy, unrestrained battles of words.
@Marko Markoko: Your comparison follows my posting, but you donĀ“t mean me, am I right?
Chiarina
2 per square mile? Meaning every two square miles you should expect to find a vis source? Vis is then everywhere. Regardless of whether there are one pawn or 10, modern Europe is about 4,000,0000 sq. mi. and Mythic Europe is even larger. So your proposal is that there are 8 million vis sources available in Mythic Europe, at the least. If they produce only 1 pawn, that's 8 million pawns of vis.
And I designed a covenant by Lake Balaton with 29 sources over 3 sqm and an annual take of 94 pawns. What's your point?
[/quote]
The point is above.
What did the players do with vis in the last saga?
You mean my saga? The saga just started. We will see.
Chiarina.
Yes, yours, sorry. In the first saga where you were vis poor, what did the magi do with the vis that they had available?
Mainly they used the vis to cast ritual spells. The group had one verditius who made some artifacts. They did not use the vis to learn the arts. This is a mechanism IĀ“d like to see sometimes in my new group. So IĀ“ll give them few books but plenty of vis and watch whatĀ“ll happen.
Chiarina.
The best way to use vis to improve Arts is to buy books. 
When you say 0-2 vis sources per square mile is that all vis sources or discovered vis sources? Because London, for example, is 607 square miles, and I use London because it has changed very little in geography since the middle ages, using the same street plans etc. Obviously more modern plumbing and electricity have been added, and the shops have changed, but the area should be roughly the same.
Which means within this one city with a probable dominion aura of some significance, you would expect to find 1214 vis sources according to that calculation. Now admittedly you did say on average and we could assume that the city is lower than the surrounding countryside, but this vis would still need to be somewhere within a days travel of London for a smooth distribution as the question suggests.
No, you're cool. And it is not as unrestrained as the List was nor as sharp. But I would say about halfway there. And sum total zero, neither good nor bad. If you have thick skin and can handle the battles, there is growth through conflict. Case in point demonstrated here. The conversation has morphed from a simple question, to a flame war (God knows why), to an introspective discussion.
A thread warmed by the flames.
To add oil to the fire: What about using the metric system?
I think vis sources are like email accounts: There are zillions of them but unless you are with the Divine (or the NSA), you know about only about a few (the ones you trade information with) and have access to maybe one or two (or five) yourself.
The difference is that creating new accounts is a lot easier than creating new vis sources.
If you really want numbers, try this:
The 4th edition Alps tribunal had a magus density based on vis, which could be used to calculate the vis density for this area:
Magi * Vis needed per magus / Tribunal size
Well, the theme of that Saga was "Nothing attracts trouble faster than inadequately guarded wealth" 
. You see, the thing is they had to develop the covenant raw. None of the vis sources they found were guarded in any way, they had to find ways themselves. And oh boy did they have trouble. They faced Hermetic raiders from Greater Alps, Rome, and Novgorod. They faced magical creatures (the Waimie), battling Fairie courts, a jealous mundane lord who was a cross between Baron d'Arques & Baron Le Cornu from Antagonists, vampires, The Knights Templar (the good guy version), the Orthodox church, rival covenants (oppidia), an infernally tainted vis source that had to be destroyed, and last but certainly not least, the political machinations of House Tremere. It got to the point where they were rolling up new grogs every night, and companions and magi very frequently. They ended up having to give up almost all the vis sources, keeping only six for themselves (the majority were given to the Transylvanian Tribunal in return for political and military protection). 
They ended up having to spend so much time defending their vis sources and themselves, they had very little time for lab work which greatly hindered them later on. At the end of the Saga, that they were happy to give most of it away just so they wouldn't have to deal with it anymore. All in all, one of the best Sagas I've run yet, and I've been playing since 1992.
I'm not even going to attempt at mathematically figuring this out, its not my style, but I will think about the question of this thread in terms of story and theme.
Basically, I would assume that the Vis we are taking about is aligned with the Magic Realm, which mean it follows the themes and needs of magic for it to function. (While all of the Realms of Power have Vis Sources the reasons and hows of them are different).
Magic is everywhere, it represents the ideal, of purity, epicness, legendary, and perfection. Because of this places that are often untouched by man have more magic than those that have been paved over and made into parking lots and other man made constructions.
Thus, places that are still super mythic (say Hibernia for example) might have more vis than places that are the most civilized as one could get it - say much of Italy.
So Vis Source density would vary based on where it is, the more mythic and magical and supernaturally focused the place is the more vis can be found. Thus the Theban Tribunal, where mysticism and magical traditions still have a major focus, would have more than say the Italian Tribunal, where thousands of years of organized, logical, civilization have made the area full of (beautiful in my actual opinion) organized paved lines and districts. The Alphs Tribunal (contrary to what the book actually says) probably has quite a bit since a lot of it is cold, frost covered, dangerous to trouble, and ignored except for the main paths and ways.
One of the things is that a magical island or a place with rich magical traditions would have a lot of vis sources. I think, for example, that Candia (Crete as we know it now) would have a lot of Vis Sources, probably at least one if not many more of each kind. This to me is especially true in that the massive many mile long Gorge that lies within has a Magic Aura of 2 everywhere.
I think that part of this question varies based on the sort of saga being told. If the saga is about magic is fading then vis sources are low in number but high in importance. If the saga is about the mythic or the ascendency or the power of magic than vis sources might be plentiful. Also, I figure vis sources are more common around sites of Hermetic covenants and Hedge magi establishments due to the presence and use of magic.
Just my thoughts on this. 
Once again, we are talking about sources, not pawns. I also said 0-2 sources psm. That means one-third are not going to have any sources, one-third will have one source, and one-third will have two sources. And note that covers all vis sources, magical, fairie, divine, and infernal. So, going by your math about 4 million vis sources, a not unreasonable amount for an entire continent plus islands.
@ talos402000
Sound interesting, thank you.
I assume the vis question was the centre of your saga, then.
Chiarina.
That math makes things downright silly unless you make vis sources incredibly subtle. If the Order of Hermes was only able to claim 1% of the available vis sources, which is kind of hard to believe in the face of their notable political dominance compared to others who would find a need to exploit Magic-aligned vis sources, then we're looking at an average of 33 sources per magus. By the guidelines of the core rules, this is an obscenely vis-rich model; where it's not unheard of for magi to have 60 pawns per year.
Bingo.