> I guess, from the comments above, that they mark out the core of the clan's territory: holy sites, steads, fields and prime grazing. The sort of stuff that the clan will fight to protect. What's left in between is the wilder non-cultivated portions, low quality grazing and hunting grounds. This being the porous portion you mentioned above.
>
> Is that the right sort of thinking?
Yep. The wyter protects the core lands and holy places of the clan. There are going to be lots of land claimed by a clan that are not protected by the wyter. And the wyter may protect areas that would not seem obviously important and ignore economically valuable places.
Jeff