DCist joins all of New York in celebrating the 100th anniversary of the New York subway system. Check out Gothamist for full centennial coverage. Though Boston may have the nation’s oldest subway line, New York’s subway truly defined what transit is. It has had more influence on American culture and notions of urbanity than any other transportation system, including D.C.’s very own metrorail, despite the slogan as being “America’s Subway.” As New York and…