What exactly is 'Layer 0?'

[Broph]

Good Afternoon,

 

I have about 4 years experience working with AutoCAD, and still (embarassingly) don't know what exactly Layer 0 is, apart from it being the default layer.

 

I have tried googling, but still not really understanding the answer.

 

Does it have to do with X-Refs & blocks etc?

 

Thanks.

[nestly]

Here is a description of Layer 0. I think Layer 0 is mostly a "left over" from early AutoCAD, but like Defpoints, it's primary use is probably so all drawings have at least one common layer, which is particularly useful for blocks. Layer 0 is also tied to dimensions (and Layer 0) somehow. I don't necessarily agree with the authors practices, but information is still useful.

[danellis]

If objects in a block or xref are on layer 0 then they will take on the properties (colour, lineweight, etc.) of the layer that block or xref is inserted on, subject to those properties being set to ByLayer.

 

This would, for example, allow one to create a "doors-existing", one for "doors-removed" and a "doors-proposed" layer, and have the same block appear differently (you might want to have existing doors appear lighter than proposed one, or have doors to be removed be dotted)

 

dJE

[CyberAngel]

Layer 0, as I understand it, is something like the world coordinate system. You must have an unambiguous origin point and set of axes, or you could (hypothetically) create a coordinate system, create a second one, then delete the first one. Just from an administrative standpoint, it would be a nightmare.

 

The name itself is a clue. You could (hypothetically again) create a few layers, delete a few, and rename a few, with the usual chaotic result. Now suppose you want a layer on which objects inherit properties--how would you specify that? Another nightmare.

 

With a layer that shares some properties across all drawings, you have a tool that lets you do things you couldn't do otherwise. Some of those things aren't as relevant as they used to be, but they're there for backward compatibility.