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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.