AutoCAD 101 – Layers (are a piece of cake…)

A lot of folks use AutoCAD every day and while doing so, use the ‘Layer function’ – but how many actually understand its full power and how to maximize their productivity by utilizing them properly?

What are Layers?

In AutoCAD, Layers are basically graphic levels of a DWG similar to a cake. Like a cake, Layers can be quite sweet if used properly. With a cake, you have your inside layers (one or more cake layers) and then you have the outer layers; the icing and sprinkles layers. With a cake, you cannot typically see the inside cake layer because it is hidden by the icing and the sprinkles layers. If the icing only covered parts of the cake, you could see everything except where the icing and sprinkles were located; this is very similar in AutoCAD. With a cake you would have to scrape (or lick) off the sprinkles and the icing to see what is underneath – are you hungry yet?, With AutoCAD you can ‘Freeze’ or ‘Turn Off’ the icing and sprinkles layers, then ‘Thaw’ or ‘Turn On’ these when your want to see them again – much less mess.

Layer Attributes

Cakes come in a variety of flavors and decoration options. Each layer of your cake has choices for flavor or color like chocolate (brown), vanilla (white), pistachio (green) or even strawberry (pink). AutoCAD has more color choices than you can possibly imagine, although with the exception of white, I am not sure I have used much of the preceding colors. The decorations also come in different looks – like sprinkles or decorative line-work, writing or doo-dads that sit on the top of the cake. AutoCAD also has similar options which include types of line work (hidden, centerline, dotted, dashed, etc…) line weights (width of lines) and doo-dads. In AutoCAD, doo-dads would typically be presented via “blocks”. Blocks are basically graphic presentations of something, like chairs, windows, doors, gears, pistons, etc… We will get a lot more detailed on efficient block usage in a future AutoCAD 101 post.

Display/Presentation Control

A powerful feature of layers is the ability to control what you see on the screen, what you plot, and how the drawing objects and lines appear for both. Working in the building world you may want to show all ‘new’ walls, doors and windows as individual colors on the screen and plot with a thicker line weight than existing walls, doors and windows. In addition, you may also want all the existing items to show up as a hidden line type while the new versions show as continuous. Layers allow you to do this very easily. The more control you want over display and plotting, the more layers you make. Keep in mind that you need to use good layer naming conventions so that it is easy to logically organize and differentiate the layers. For instance, you may want to name all layers pertaining to “Doors” with “Door” at the beginning of each layer name; Door-New, Door-Existing, Door-New-Header, Door-Existing-Header, etc… or maybe group all “New” and “Existing” layers; New-Door, New-Window, Existing-Door, Existing Window, etc… Whichever method you use, spend some time thinking about it, considering multiple scenarios and discuss with your fellow CADD folks or possibly with some outside experienced users in your industry. Another option is to adapt an industry layer standard and follow it. A good one is the National CAD standards layering system. The National CAD Standard is a collaborative effort in the United States between the National Institute of Building Sciences, the American Institute of Architects, and the Construction Specifications Institute, to create a unified approach to the creation and collaboration of building design data by means of building information modeling and integrated into CAD software such as MicroStation and AutoCAD. You can find more information here: National CAD Standards

An older PDF version of the layers can be found here: Layer Guide

Special Layers

AutoCAD has a couple of special layers that you will want to know about – Layer “0” (zero) and Layer “Defpoints”. It is important that you not only know about these layers, but how you should use them. We will get away from the Cake analogies for a bit and focus more on some technical magic that these layers can perform.

Layer 0

Let’s start with Layer “0”. Layer 0 is a default layer that exists in all drawings and should not be ‘frozen’ or modified in any way. The most powerful use of layer 0 is for creating blocks. Blocks that are created on layer 0 will assume the attributes of the layer that they are inserted on, which is why I often refer to layer 0 as the chameleon layer. So what does this mean and how is it useful? When a block is created on layer 0, it will be white and have a continuous line type (default layer 0 properties). When this block is inserted on another layer it will change to the color and line type assigned to that layer. How is this useful?

A Practical Example:

Let’s say you’re an interior designer or an architectural CADD technician and you are creating a furniture plan – better yet a furniture renovation plan. For this plan, you need to show the old and new locations of furniture that is being moved around as well as what is being removed from the building entirely. As you are a smart CADD technician, you have created blocks for all your furniture pieces which include desks, chairs, sofas, file cabinets and computers.

  • Scenario #1: You created all of these items on a layer called “Furniture” with the color of Red and the line type continuous. You start by showing your existing furniture plan on the “Furniture Existing” layer and place all your furniture on this layer. You then create “Furniture-Removed” and “Furniture-Relocated” layers, so that you can isolate the old new and removed status of the furniture layout by freezing and thawing layers. You then create three views on the same drawing showing the Existing, Relocated and Removed layouts. Since the furniture was all created on the furniture layer, all versions of the furniture will be red with a continuous line type, so you will have to note each items or hatch over it to indicate its status. Another option is to create an Existing, Removed, and Demoed version of each block with different colors and line types, or just explode them and change their properties. (You wouldn’t do that would you?!?!) The bottom line is that it will require more work to be clear.
  • Scenario #2: You created all of the furniture items on layer 0 and left the default layer properties of White and continuous. You then created the same layers as in Scenario #1, but the “Furniture-Existing” layer is Red/Continuous, the “Furniture-Relocated” is Blue/Continuous and the layer “Furniture-Removed” is Grey/hidden. As in example #1 you start by showing your existing furniture plan on the “Furniture-Existing” layer and place all your furniture. You then create the “Furniture-Removed” and the “Furniture Relocated” layers. Since the furniture was all created on layer 0, when the items are inserted in to each layer, it will change color and line type so that it can be easily differentiated. This would at a minimum reduce you to only having to do two views (Existing and Renovated) with each piece of furniture on the “Existing” plan being on the appropriate layer for whether it is staying, relocated or removed.

In case it is not clear, the reason for the red vs blue layer colors in scenario #2 is because the red and blue will be easy to differentiate on the screen and will plot as different thicknesses. If you do not use color standards for plotting, you could use the Layer “line weight” option instead for each layer. Hopefully you have some documented standard for plotting.

Layer Defpoints

The second specialty layer is “Defpoints”. Defpoints is created each time you create a dimension in your drawing when you are using associative dimensioning.  AutoCAD creates nodes or points where your dimensions intersect drawing entities. You can also create the defpoints layer manually. The power of defpoints is that anything that shows up on it will be viewable on the screen but will not plot. This feature has been used by some to such an annoying level that people are now in the habit of freezing defpoints so that they can see what they are doing. Newer versions of AutoCAD (since 2000)  now include a Non-plot variable in the Layer dialogue to allow you to select any layer as non-plotting but viewable.  The most common usage for defpoints is for creating clip edges for xref clipping, viewports in paperspace or hatch boundaries. It would be a good idea to stop this practice and add a few new layers to your standards to address these items individually. Please STOP using defpoints for notes and sketches!  It was mentioned earlier that you should not modify or freeze layer “0”.  The reason you do not want to layer 0 is that it has a bond with defpoints.  If you freeze layer “0” and have linework on layer “Defpoints”, you can see but cannot edit or select anything on that layer – the two are linked.  This will drive you crazy initially.  Of course if you follow all the rules and do not draw on either one or modify either one – you’ll be fine.

Summarizing the important items from this post:

  • Create Blocks on Layer “0” – Nothing else (chameleon layer)
  • Do not Draw on Layer “0” or Defpoints”
  • Set all your objects color and linetype to “Bylayer”
  • Do NOT use Defpoints for viewports, notes, etc..  make a separate layer and set it to a  “non-plot” layer
  • Use as many layers as needed to make the look and plotting controllable
  • And Finally – Do not draw on Layer “0” or Defpoints”

Wrapping Up
Just because you have been doing something for years, it does not mean it is correct. Unfortunately due to the fact that many companies do not see the importance of training and many schools have unqualified instructors, many people have learned much of what they do on the job from others who learned on the job, who learned from people that did not know what they were doing. Open your mind to new ideas and better ways of doing things. Put some thought in to how you setup your drawings – in many cases, especially for architects many people have to work with what you create – and trust me, it can be very frustrating. As the main point of this blog states: It’s time to re-evaluate how “you’ve always done it”…

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