CADcaster

Every time you create a new drawing, you will see a default layer: Layer 0. You can’t delete this layer.

Then when you define layer properties such as color, line weight, etc, you will see ByLayer and ByBlock property. Most of you might already know what is ByLayer means. But do you also know what is ByBlock behavior?

In a nut shell, here is the explanation

• Layer 0 is a default layer. You can create geometry in your blocks using this layer. When you insert those blocks, they will use active layer. When you move this block to different layer, the objects in it will use the layer and ignore Layer 0.
• When you define object properties (color, line weight, etc) to ByLayer, all of it properties will use the same properties as it’s defined in layer properties.
• When you create geometries in your block using ByBlock, then you can override it’s properties after the block has been placed.
• When you create geometries in your block other than ByLayer or ByBlock, then you can’t override them after your block has been placed.

Confused? Let’s create some example to comprehend this better.

Open your AutoCAD, in a new file create two layers, you can give them any name. Set different color and lineweight so we can easily distinguish them later.

Now we will create 4 objects, in this example I use circle.

• First circle use layer 0, color: by layer, line weight: by layer
• Second circle use layer 0, color: by block, line weight: by block.
• Third circle use layer 0, color: red, line weight: 0.5 (we set this high so can be easier to see).
• The last one use layer 1, color: by layer, line weight: by layer.

Create 4 blocks from each of the circle. Now select all those four, then change their layer to Layer 2. You can see block 1 and 2 use the layer properties, but block 3 and 4 still using it’s own properties.

Now override the color and line weight. Use color green, and line weight 2. You can see that the only block using the overridden properties is block no. 2!

Only block no.2 using the block properties, because we set it the geometry properties to by block.

Now freeze Layer 1. We can see the block no. 4 disappeared, because the object in it was created in Layer 1.

Unfreeze Layer 1, so we can see block no. 4 back. Now freeze layer 2. Remember, we have moved all of the blocks to Layer 2. What happen? All of the blocks disappear, including block no. 4! This block also disappear because the block itself using Layer 2. When we freeze Layer 1, the block is actually still showing. But the geometry inside it will be disappeared. This will be clearer if we have another object with different layer in that block.

Unfreeze Layer 2, then freeze Layer 0. None of the blocks is disappear! Remember that we created geometry in block 1,2, and 3 using Layer 0? They will ignore that layer and use the new layer properties.

If you want to understand more about this behavior, try to create more objects in your blocks. Set them to different properties. And play some more with layer properties. But I hope this is clear enough

Source: CAD Notes – Layer 0, ByLayer and ByBlock
Go to Source: CAD Notes