Near the north end of Manhattan's High Line Park there is a building painted with a mural by the french artist known as JR. Although the full mural, with its portrait of a member of the Lakota tribe, is interesting, I was taken by the background of giant polka dots. The discipline of their regular spacing and the black-and-white boldness banish the sense of whimsicality or flightiness that one often associates with polka dots. And it just looks really, really cool against a bright blue sky.