As far as I can determine, it's derived from a poll taken by the Public Religion Research Institute, which claims to be nonpartisan. My instinct tells me their a leftist outfit but, that said, as one who frequently traveled, it does seem right. It's no surprise that Portland, OR leads the list of this rogue's gallery of places that are anti-God. It has a lot of hippie types and good number of the thug element (I almost got mugged there several years ago). Plus Oregon allows "doctor" assisted suicide, a direct repudiation of God's Laws.
ALL of my family in Oregon are devout Christians...and there are more and more of them to come , as they grow their families... Too bad for the Portlznd crowd who are killing theirs!