Sauvie Island is the largest island in Oregon. It lies just north of where the Willamette and Columbia river come together.
The island is the northernmost point you can reach on Tri-Met, Portland's bus service. It is rural, but it has several stores, and in summer, is a frequent destination for Portlanders wanting to take a few hours of vacation.
The Island, which is about the size of the entire Eastside of Portland has only a few thousand inhabitants, due in part to the fact that it is surrounded by two large rivers, and is never higher then 10 meters above them. In other words, it is very likely to flood, as it did in the great 1996 Oregon flood.
Although not a populous or economically important area now, before large scale settlement by Europeans, Sauvie Island was a great meeting place for 'Indians', as it was at the convergence of the two large rivers.
While the southern parts of the island are mostly used for farmland or residences, (including, as the softlinks seem to have it, the Pumpkin Patch, a large farm for people to go and pick their Halloween pumpkins), the northern parts of the island are usually too swampy and dotted with small lakes to be of much economic use, so instead they are kept as a wild life refuge.
And BTW, it can be pronounced either So-vee or Sah-vee.