If you're doing something that doesn't have a precedent --- and making an island the size of Ireland and claiming it for one covenant has no precedent -- there is by definition not going to be anything in the Peripheral Code (which consists entirely of Tribunal rulings) on the issue.
The legality will accordingly be decided entirely by a majority vote at Tribunal if/when the issue comes up before it.
Whilst it is not exactly analogous, the Great Tower from Hermetic Projects is a very similar concept, of creating a very large thing that neighbouring monarchs will be very interested in, much of what it points out there could be used for a slowly growing island.
From the same book elements of the Hermetic shipyard are likely to be useful in order to get the ships needed to populate a place that big.
That said, simply dumping stone or Earth into the sea until you have a landmass is not enough to make a habitable island. Look at the Reclamation projects of the Netherlands Land reclamation in the Netherlands - Wikipedia which started in the 14th Century.
Also consider things like the soil, which if you want anything to grow there would need some source of fertility. fresh water sources (Making a spring is pretty easy with Creo Aquam rituals on a small scale, but for an entire landmass you would probably initially need to summon rainclouds to ensure that there's something for your people to drink and to start the formation of rivers rather than flood planes.
It's also worth considering that a new landmass would probably not have any Vis sources initially. Magic Auras would primarily form around the ritual activity of the Magi themselves (Realms of Power: Magic), which could then be used to house magical beasts.
On the other hand, magically generating large amounts of land from the sea would almost certainly require very expensive ritual Creo magic.
The most relevant published material is the "Island of the Magicians" chapter of Transforming Mythic Europe, which (as one would expect) covers all those issues already.
I think it's worth pointing out that you can absolutely create groups of springs
You can absolutely, but across an island the size of Ireland, that might not be very useful unless you are creating groups of springs at Arcane connection ranges which might prove prohibitively high level.
How do you create springs, I thought it would require regular ritual castings to keep the water going.
Sorry, responded to the wrong person, meant to respond to Wingsday
No worries.
One of the guidelines in the corebook is:
CrAq 4: "Create a spring with a low rate of flow."
CrAq 5: "Create a spring with a high rate of flow."
CrAq 10: "Create a geyser with a very high rate of flow."
You are correct in that it would require a ritual, but you are permanently creating a water-source, rather than a finite amount of water. So it wouldn't need to be done again unless the spring dried up for some reason.
I suspect that this is an artefact of the Medieval paradigm in which the intricacies of hydrology were not understood and so springs were believed to be sources of water rather than outlets of subterranean water flows. As there are other places in the medieval belief system where things are believe to spontaneously generate. (The generation of bugs from decaying substances for example)
makes sense, thank you
Range is to the nearest part of the Target, so you only need R:touch for this spell(arm5, p111). You may need arcane connections though, ysmv. Also you can move springs with formulaic (or spontaneous) reaq.
I see no reason to presume this is a permanent spring. Just like when you create a horse, the horse is not permanent. I ruled that the spring is temporary, so the spell needs to be recast annually to re-create it or somesuch.
I ended up instead instilling a ReAq permanent effect to teleport water from a lake, using an arcane connection to it.
YSMV
That's a really weird ruling imo, using rituals explicitly creates a natural and completely real example of the spell target. and like, normal springs certainly vary over time, often changing flow, sometimes moving, sometimes disappearing, sometimes appearing or reappearing for mostly unknowable reasons. But lasting a year and then abruptly disappearing is definitely not typical spring behavior
I fully agree with Wingsday here. The Spring is "permanent" in the same way as any natural spring.
Springs do wax and wane and sometimes exhaust themselves but there's nothing to suggest a year duration.
Meanwhile transporting water from a lake (presumably in Stonehenge?) Would require either regular spellcasting or a magic item.
Ritually creating springs is a thing in ars magicka, much like Perdo permanently dries springs.
Creating a lesser enchantment that creates a spring or 3 at moon duration (or a spell that does the same if you're desperate) is probably more practical for a normal covenant, but imo the island of magicians is probably the exact niche for the ritual use
Generally speaking, creating water with a temporary duration has more badvthan good in ars. If you rely on fake water for a moon, when the moon duration expires, you're likely to die from thirst. Admitedly, if you rely on that a day every week but supplement with real water for 6 days... You may just be thirsty. I suspect the same is true for plants and animals. Relying on moon duration water os a great way to kill the crops and trees you're planting, and the animals you might raise on the land.
You're creating a spring in this case though, which the water emanates from meaning the water is mundane, akin to mundane light emanating from a magical fire. I believe there's a discussion in one of the books on the mundanity of surface water emanating from a magical rain storm, but I could be wrong about that it might have been on here instead
Yes, but "The components of the group must be close together in space."
So you can't create a Group of springs across an entire island.
That's fair enough I suppose, if rather vague. How close is close enough? If this distinction is primarily about being able to discern a group, I would argue that you may spread objects much wider if there are no similar objects nearby, as one would assume to be the case with springs on a newly ritually created island. Regardless, there's nothing stopping you from moving them with reaq or muaq(fo)/mufo(aq).
Alternately a large spring at higher elevation could be diverted into multiple streams.
Hear hear!
I second what Silveroak wrote. Seems reasonable and useful approach to the matter. Also solves some aforementioned problems.
Good thinking! I like how your brain works 