Polygonal chain
（重定向自Polyline）
In geometry, a polygonal chain is a connected series of line segments. More formally, a polygonal chain P is a curve specified by a sequence of points 
called its vertices. The curve itself consists of the line segments connecting the consecutive vertices. A polygonal chain may also be called a polygonal curve, polygonal path, polyline, piecewise linear curve, or, in geographic information systems, a linestring or linear ring.