The definition of T:Boundary explicitly states a physical boundary of some sort, it can be natural or man-made. So country and Tribunal borders aren't really an option here.
That's why GHW Bush (the First) made such a big deal about drawing a line in the sand, so he could unleash his wizards...
After I checked the book, I think it actually doesn't need a T:Boundary at all.
In this case, we're talking about a spirit ability, not a Hermetic effect, that says the following:
Since it refers to the size of the area but not to a specific target, and because it makes little sense for spirits whose Might is less than 30 to require a building to have a Presence (genii loci usually don't), I don't actually think that this boundary actually means T:Boundary.
(Also, if I manage to build a Daimon up to Might 90, this means that he can have a Presence that covers the entire world in a Magic 5 Aura, whether or not we go by the strict definition of Boundary. Anyone want to take bets on how long this lasts before God smites this upstart titan?)
I would expect that the area of influence of a kingdom's patron spirit would expand or contract as the kingdom grew or shrank.
Hi,
In Medieval/Mythic Europe, the continent of Europe is bounded by the Mediterranean (which divides it from Africa) and the River Don/Tanais (which divides it from Asia). The Nile divides Africa from Asia, resulting in the classic T&O map with Jerusalem in the centre. Thus you could say that there is a boundary around Europe, as long as you allow that the Don is as long as it was thought to be, and extends northwards to join the Volga watershed.
Mark
I don't see a problem with allowing a supernatural creature to use fuzzier boundaries for one of their powers.
But I'd suggest that allowing it for Hermetic magic can have perverse results. You could end up with a magus inventing a low-Base effect with a pumped up Boundary target and affecting all of Europe. Say, CrIg 2 to ignite something highly flammable. +1 Touch +4 Boundary +10 size = level 65 ritual to set all of Europe ablaze.
But a magus would have to WALK the boundary, wouldn't they?
Boundary walking is only mentioned for the Aegis, and the language there is even suggestive that it is optional. Touching the boundary is sufficient.
Europe isn't highly flammable. Unless you mean in a political sense.
On the other hand, you can definitely use a variant Pilum of Fire at CrIg 10 for +15 damage, +1 Touch +4 Boundary +10 size, CrIg 85 ritual to set Europe ablaze, or "ignite anything even barely flammable" for the same. But extending "Boundary" to large enough areas, with or without boundaries, already gets ridiculous just because scientific notation gets very ridiculous very quickly, and determining how big a Boundary should be affectable by a magus is a pure saga call (is nuking the isle of Britain any more sane?). (A few more size increases and the magus can light the world on fire, and I have to agree that Ouroboros/Jormangundr is a valid Boundary if nothing else is; so is the Limit of the Lunar Sphere, if you really want to be pedantic...)
Wow, can't wait to point this out to my SG, we have always played it like a ring/circle and needing to be traced 
Ring and circle DO need to be traced, it's not the same as T:Boundary.