A line is a single straight line segment defined by one start node, one end node and no other nodes. A polyline is also defined by one start node, one end node and no other nodes, but is made of two or more consecutive straight line segments. The connections between the constituent line segments of a polyline do not appear as nodes in the vector map.
Polylines provide the most appropriate representation of curved lines when it is important that nodes serve to define topology rather than geometry. Curved lines are usually digitized as polylines, but these are sometimes broken into their constituent straight line segments during conversion from one data format to another. v.build.polylines can be used to rebuild such broken polylines.
If the lines that make up a polyline are of different types, then v.build.polylines will set the type from the first constituent line.
Category number(s) are assigned to a polyline based on cats parameter.
v.build.polylines correctly handles input vector maps containing lines, boundaries, centroids and points. Lines and boundaries will be converted to polylines of the desired type. Areas are only guaranteed to be preserved if the constituent lines of the polylines that define them are all boundaries in the input vector map.
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