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For a guy who doesn’t live in one, Mark Stein sure knows a lot about states. The D.C. resident’s book, How the States Got Their Shapes, delves into the geographic biographies of the 50 messed-up pieces of land that made the cut——with the District’s wonky diamond thrown in for good measure. The book promises to explain the United States’ most pressing border mysteries: Michigan’s floating peninsula, Texas’ bigness, West Virginia’s creepy finger up Pennsylvania, and Delaware. The history of our 4-million-square-mile jigsaw puzzle is a bit of a departure for the local boy: A playwright and screenwriter, Stein’s previous claim-to-fame was writing the 1992 Steve Martin—/Goldie Hawn vehicle HouseSitter. Thankfully, Stein’s better at tracing border lines than he is scripting wacky squatter comedies. This volume isn’t just smarter than his film work——it’s funnier, too. Stein discusses and signs copies of his work at 7 p.m. at Politics and Prose, 5015 Connecticut Ave. NW. Free. (202) 364-1919. —-Amanda Hess