Polylines are objects formed by line segments, arcs, or a combination of both. And although we can draw independent lines and arcs that have as their starting point the last point of another line or arc, and thus create the same shapes, the polylines have the advantage that all the segments that form them behave as a single object . Thus, we often have cases in which it is preferable to create a polyline that different segments of lines and independent arcs, especially when corrections have to be made, because it is easier to edit changes in a single object than in several. Another advantage is that we can define an initial and an end thickness for a single segment of the polyline and then re-edit this thickness for the next segment. In addition, the construction of polylines assures us that the starting point of a line or arc segment is attached to the anterior segment. This union will form one of the vertices of the polyline and even when we modify it by stretching or displacing it (as we will see later), the union between both segments continues to exist, which allows us to create closed contours safely, which has several advantages that will be appreciated later: when we see regions in this same chapter and when we study the editing of objects and shading.
As the polylines are segments of lines and arcs, the corresponding options allow us to define the parameters that we already know to create lines or arcs in the individual. When we execute the command to create polylines, Autocad asks us for a first initial point, from there we can decide if the first segment is a line or an arc and, therefore, indicate the necessary parameters to draw it.
Once we have drawn two or more segments, the options in the command line are to close the polyline, that is, to join the last drawing point to the first one. The polyline closes with an arc or a line depending on the nature of the last segment drawn, although it is obvious that it is not mandatory to close the polyline. Finally, consider that it is possible to change the initial and final thickness of each segment of the polyline, increasing its possibilities in creating shapes.