lines and poly lines

what is the difference between a line and a poly line and when should I use a line and when should I use a polyline? thanks

A LINE is just that, a line with a start and end. Nothing more, nothing less. A Polyline or PLINE is a composition of lines, and each segment start/end is attached to the next. A PLINE can even have curved segments, and a PLINE can also be "closed", such as a rectangle. Once closed, you can calculate areas, and also can be used as a profile for creating 3D objects.

When should you use them? Well, when you EXPLODE a PLINE it converts all straight segments to a regular LINE and curved segments to an ARC. The most common practice is to always default to use PLINE because it's functionality is much more valuable than a normal LINE.

There are many more advantages of PLINE as well. I'm sure others will reply with their opinions. Welcome to CADTutor.net.

for hatch boundaries use closed polylines.......click, click, click, click, c (for close)

A continuous multi-segmented polyline is a single object and can be selected, moved, copied, or erased all at once. Unlike a bunch of connected lines, which are each separate objects, and must be selected and modified individually.

Welcome to CADTutor. One of the most useful features of a polyline is that it is always drawn FLAT, by which I mean it will be parallel to the current UCS. The Z values will be the same for every point on a polyline. At times we may not want that, and can choose to create a 3D Polyline instead. Rarely do I use the LINE command, maybe a few times a day. I must use the polyline command thousands of times a day.

Welcome to the CADTutor forum.

A line has it's end points described by two sets of 3D coordinates (X,Y and Z) a normal polyline (LWPolyline) has it's end points and any intermediate vertices (nodes) described by 2D (X and Y) sets of coordinates and as Dadgad said they are always flat. You can however have a 3D polyline where it's end points and any intermediate vertices are described by sets of 3D coordinates. But unlike a normal polyline a 3D polyline cannot contain any arcs as described by StykFacE. To create a 3D polyline from a 'chain' of line segments use the "JOIN" command or draw a 3D polyline directly using the button on the Ribbon.

The only time I use LINE is for drawing Deferred Tangents, for some reasons PLINES do not work accurately.

Here is an older Polyline vs Line thread.