Many Vis sources require a specific set of actions to be undertaken at a specific time to harvest vis successfully. Additionally, some Regios require a ritual action in order for non-natives to enter them.
Sometimes discovering this lends itself to an obvious story but sometimes this is best handled as a downtime activity. What rules have you applied to discovering the necessary actions or rite? I'm wondering if there is a parallel system similar to seasons devoted to investigating enchanted items or experimenting.
That side has been interesting, especially since if you don't look for anything in particular, you're going to end up with a veritable library of low level Auras; and I can only assume that magical beasts are automatically found in level 4 auras when you do this? On top of that, magical beasts certainly have a weird ratio of vis to Might compared to the official rules.
Thanks for the recommendation, but there are rules for Vis hunts in the RoP: Faerie book already which resemble those described in the link.
I'm specifically speaking of finding sources where there is a harvest ritual like those described on page 4 of the sample covenant, Semitae Errabunda (atlas-games.com/pdf_storage/Semita.pdf):
Example 1 - If a fire is kindled on the top level of the regio and carried out through that level, and then brought back in through the mundane world and the bottom level, before being allowed to burn out in the top level, the ashes contain a pawn of Ignem vis. The fire cannot be transported by magic at any point, but the covenant still manages to do this about once per season. This source can produce no more than four pawns of vis in a single year.
Example 2 - A natural mirror in a cave on one level of the regio reflects the true feelings of anyone who looks into it. If someone who is deeply sad, but successfully hiding their emotions, looks into it, five of the tears cried by the image bead on the mirror’s surface, and each drop contains a pawn of Intellego vis. This source produces no more than five pawns of vis per year.
Clearly a fair amount of research would be required to discover all the preconditions needed to harvest the vis in these circumstances. This sounds like a seasonal activity to me, similar as I mentioned to investigating enchanted items.
I don't have any answers for you. I just wanted to say I think the question is really good and worth pursuing. I could see doing it something like the work to understand an enchanted item, but figuring out the numbers could be tricky and in many/most cases this really couldn't be done in a lab, though perhaps samples of things could be brought back to the lab and researched.
I don't find anything in RoP: Magic about this, nor so far in the main rulebook.
As an investigation into Regios, if nothing else comes up, I'd consider adapting the Investigating Enchantments rules, p. 100, so that the target power is the Aura in magnitudes - Regio/Aura 1 is Level 5, and so on. For some, or many locations, this is impractical - a monastery is not likely to let a mage conduct arcane investigations openly for three months. I suspect magi lean heavily on InVi spells to just step through the threshold.
Vis sources are trickier, I think. Some vis sources described don't lend themselves to giving a clue that the vis source exists. InVi magics to detect vis are pretty easy, for manifested vis, but finding out that vis will manifest when you dance widdershins around the standing stone while naked and crowned by a wreath of flowers under the first summer full moon, absent an example...
I believe Nature Lore (Originally Forest Lore, from Guardians of the Forest?) is your best bet. Get a companion who is good at it, and he can just "find Vis" at rank 3. One assumes that's how the locations are found, as well as the tasks to get the Vis......