In the map of Isola taken from Plant Tycoon, there does appear to be a place for the East side, it's just very difficult to see. It appears between the pocket watch and what appears to be a magnifying glass.

As for the center of the island, it's possible that a tribe could be surviving in the mountainous area that looks a tad like a cavern or if there is another clearing, it may be being hidden by the trees or the mountains.

I would add a copy of the picture but I can't save things on this computer. So I will give you the link to a post with the information. It's found here.

That said, I can't wait to see VV3 and all of the games they are going to release in the future.