What is the polyline command in AutoCAD?

In AutoCAD, the Polyline command, activated by typing PLINE or PL, is a fundamental tool for creating 2D geometric objects. It allows you to draw a sequence of connected line and arc segments that are treated as a single object.

Understanding the Polyline (PLINE) Command

The core function of the PLINE command, as stated in the reference, is that it Creates a 2D polyline, a single object that is composed of line and arc segments. This is the key difference compared to using the standard LINE command.

PLINE vs. LINE

• PLINE: When you use PLINE, all the segments you draw sequentially form one continuous object. If you select any part of the polyline, the entire sequence of connected segments is selected.
• LINE: When you use the LINE command, each segment you draw is a separate, individual object. Selecting one line segment only selects that specific segment.

This distinction is crucial for editing and manipulating your drawings efficiently. Editing a polyline allows you to modify all its segments together, whereas with individual line segments, you must select and modify each one separately.

Let's look at a quick comparison:

Feature	Polyline (PLINE)	Line (LINE)
Object Type	Single object	Multiple individual objects
Segment Type	Can include line and arc segments	Only creates straight line segments
Editing	Edits apply to the whole object	Edits apply to individual segments
Width	Can have a consistent or varying width	Has no intrinsic width property (width is visual, not geometric)

How to Use the PLINE Command

Using the PLINE command is straightforward:

1. Type PLINE or PL in the command line and press Enter.
2. Specify the start point for your polyline.
3. Specify the next point. You can continue specifying points to create line segments.
4. While drawing, you'll see options appear on the command line or dynamic input. Common options include:
   • Arc (A): Switches to drawing an arc segment connected to the previous point.
   • Halfwidth (H): Specifies half of the total width for the segment.
   • Width (W): Specifies the total width for the segment (start and end width). This allows you to create thick or tapering polylines.
   • Length (L): Draws a segment of a specified length at the angle of the previous segment.
   • Undo (U): Undoes the last segment drawn.
   • Close (C): Closes the polyline by drawing a segment from the last point back to the start point, creating a closed loop.
5. Press Enter to finish the command when you are done drawing segments.

Practical Benefits of Using Polylines

Using polylines offers several advantages in AutoCAD:

• Simplified Editing: Since all segments are one object, you can easily move, copy, rotate, or scale the entire shape as a single entity. Grip editing allows you to modify vertex locations efficiently.
• Consistent Properties: You can apply properties like color, layer, or lineweight to the entire polyline object at once.
• Defined Width: Polylines can have a specific, uniform, or varying width, which is useful for drawing thick lines, roads, or filled areas.
• Boundary Creation: Polylines are often used to define boundaries for hatching, area calculations, or creating regions and 3D objects.
• Joining: You can use the JOIN command to combine individual line, arc, or polyline segments into a single polyline object, provided they are coplanar and their endpoints meet.

In essence, the PLINE command is a powerful tool for creating unified shapes composed of connected segments, providing greater flexibility and efficiency in design and editing workflows compared to drawing individual line segments.