* layer 0
Layer 0 is the default layer of every drawing, which could not be deleted. There are some special properties of layer 0. Please see another blog post to review the differences between layer 0 and other layers.
* Layer Defpoints
Some users have noticed the layer Defpoints because this special layer often comes from nowhere and users who know it will take advantage of its special properties while others who don’t know its properties will cause problems by putting objects on it.
The CAD system will automatically create Defpoints layer as long as you creates dimensions — this layer is used to place definition points of dimensions. Well, you may be asking what a definition point is. A definition point are several key points of dimension that are used to define and adjust dimensions. When we turn on the node option in the Object Snap, the nodes of dimensions that we snap are actually those definition points.
What makes Defpoints layer unique is not that it’s created automatically by CAD system but that this layer is set not to be plotted and we can’t change this setup.
If we accidentally place geometric objects on this layer, those objects will literally disappear when you plot the drawing. Some users therefore put objects that they don’t need to plot such as viewport boundary on this layer.
* Layer Filter
Layer Filter is a very useful tool and we can use it to find layers that meet our criteria.
Open the Layer Properties Manager, and click the New Property Filter, a window will pop up, as shown in the following picture,
* Layer States Manager
Sometimes we need to repeatedly turn on/off/lock/unlock layers, we can save those layer states and when we need to use them, just restore them. CAD also provides Layer Previous to undo the last change or a set of changes made to the layer settings, as shown in the following picture,