Represents a Polyline in an ESRI shapefile as a List of
GisParts. A Polyline is just an ordered set of vertices of 1
or more parts, where a part is a connected sequence of points.
A river including its tributaries might be represented by a
Polyine, for example, where each part would be a branch of the
river.
Created: Sat Feb 20 17:19:53 1999