The best breeds of cows I’ve found for this type of project are the Ayrshire and Holstein. They have the best markings that I’ve seen thus far to use for mapping purposes:

and

These two are only models taken from the web (cuz I’m lazy), and not the cows I’ve used, but look at the patterns on them. There’s great potential on both of these girls! Maybe not fit for a full archipelago, but man, there’s definitely some island action happening in there. :) The pattern in the lower right region of the bottom cow is a very nice bay or possibly just a cove with a small island off-center, while the youngster up top looks more like the archipelago type to me. But, you know — with the help of Photoshop, the imagination can just go wild.

So far, I have two working continents, and I’m on the search for more cows!