Polylines Versus Lines
Polylines are different from the line segments created by AutoCAD’s LINE command. Polylines are treated as single objects and can include both line and arc segments connected at their vertices. AutoCAD stores information about the vertices, and you can access this information and edit the appearance of the polyline.
Polylines offer two advantages over lines. First, polylines are versatile; they can be straight or curved, thin or wide, and even tapered. Figure 8.1 shows some of the various forms a polyline can take.
Figure 8.1. Polylines can assume various useful forms.
Second, editing polylines is easier: You can select any segment of a polyline, and all other segments will be also selected because all segments are connected. This makes editing operations, such as moving and copying, faster and more accurate. Objects drawn with lines and arcs may appear to be connected but, depending on how they were drawn, may actually have gaps or discontinuities that make it difficult to use them as boundaries for cross-hatching.