It's fake. Not only has the ARS posted this fact on their website, but Snopes has already busted it, and the map itself doesn't even make sense (why would it ONLY fallout TOWARD the US??), the units used are wrong (Rads? On a map from Australia?? Seriously??? Someone's been playing a little too much New Vegas), and the amounts of radiation specified are so high that even the yellow area would cause second degree burns. You'd have to drop an actual *bomb* to cause anywhere close to those numbers.
If you see or hear anyone taking this map seriously, please kick them in the ass, HARD, and force them to put their iodine tablets BACK ON THE SHELF.