Computer Studies
 Knot Making


Layers are arguably the most powerful tool used by graphics programs. But what are they?

You can think of layers as transparencies. Look at the picture of the coat of arms below. You see one picture composed of a blue background and a red coat of arms with black borders and a black fleur-de-lys symbol. Still, just one picture.

Now have a look at the following picture which explains how the coat of arms has been composed of three different ‘transparencies’. The bottom transparency contains the blue background, the middle one contains the red shield and the top one contains the border and fleur-de-lys. The proper name for those ‘transparencies’ is: Layers.

Drawing on multiple layers as opposed to one layer has many benefits. First of all, it reduces clutter and confusion by making everything more organised. Imagine that you are drawing a plan of a house for example; you can draw the base map (walls) on one layer, electrical wiring on another, plumbing, furniture and so on and so forth. In AutoCAD, every layer is given a name and can be color coded for easy recognition. You can turn a layer on and off as required among other options.

Managing layers

Let us explore how the principle of layers works specifically in AutoCAD. Layers can be managed from the Layer Properties Manager dialog box. This can be accessed by choosing ‘Layer…’ from the Format menu, by selecting the icon from the layers toolbar (ACAD2008) or layers panel (ACAD2009), or typing ‘layer’ or ‘la’ in the command line.

From the Layer properties manager you can create new layers, assign colors and linetypes to layers and perform other operations.

Every time you start a new drawing you will have a default layer named ‘0’. To create more layers, choose the ‘New’ button. A new layer named ‘Layer1’ is created and its name is selected so that you can rename it immediately. If you wish to change the name of a layer that is not selected, click on it, select the current name and type the new name. When you name layers, make sure to assign names that are relevant and will help you recognise the layer later on. It is not unusual to have more than twenty layers in one drawing and with so many, if you assign names that are not related to the content of the layer, you will end up with a lot of confusion. There is also more information available about the layers next to their name such as their color, linetype and lineweight that can be changed.

The flange example

Let us work out an easy example by drawing a flange using three different layers. Start by opening a new drawing and create three layers in the ‘Layer Properties Manager’. Name one of the layers ‘Outline’, another ‘Center’ and the other ‘Hidden’. Select the color of the Center layer; the small black square ACAD2009 or small white square for ACAD2008. A window like the one below will appear. Select the red color and click ok. Repeat for the Hidden layer and choose blue.

Now click on the word continuous under linetype and you will be presented with the ‘Select Linetype’ window. Click ‘Load’ at the bottom of this window and you will be presented again with another window called ‘Load or Reload Linetypes’. Scroll through the various linetypes and select an appropriate one for the layer you have selected. Click ‘ok’. The linetype is loaded into the previous window. Select this linetype again and click ‘ok’ once more. Do the same for the other layer and close the Layer Properties Manager.

Now have a look at the Layers panel or toolbar (shown below). The ‘Layer control’ drop down list still shows layer ‘0’ and this means that if we are to draw anything it will be drawn on this layer. In AutoCAD terminology we say that the current layer is ‘0’.

To make another layer current, click the small arrow at the right hand side of the drop down list and choose the layer. That layer will be displayed in place of layer ‘0’ to indicate that it is now current.

So now we know enough to draw our exercise. Have a look at the following diagram and draw a similar flange using the commands learnt so far. Make sure that you draw the various lines involved on the proper layer as this is the whole scope of the exercise! The dimensions are conveniently marked in green, but if you want you can draw using different dimensions.

Finally let’s explore some of the options we have just because we have drawn on different layers. Get back to the ‘Layer properties manager’ or the ‘Layer control’ drop down list in the Layers panel. Notice that next to every layer name on the left hand side there are a number of icons.

The first icon is a bulb. This is a toggle switch that switches a layer on or off. This switch simply allows the layers that are switched on to be displayed and plotted/printed, and hides layers that are turned off which will also not be plotted. You can also turn the current layer off and even draw on a layer while it is off!

The second icon is the Freeze / Thaw toggle. This is almost like the on / off toggle but with a few differences. When a layer is frozen it is not displayed, and it cannot be modified. This means that you cannot freeze the current layer and you cannot draw or perform any kind of editing on layers that are frozen.

The third icon, ‘Freeze/Thaw in current viewport’ allows layers to be frozen or thawed in various viewports. This will be covered in a later tutorial when we get to using viewports.

The fourth icon is the Lock/Unlock layer toggle. When you lock a layer, it will still be visible but you cannot edit the drawings on this layer. This is very useful if still need to see the layer but do not want to accidentally modify the drawings it contains. The current layer can be locked and you can still draw on a locked layer, but you will not be allowed any editing. Locked layers are also plotted/printed.

In the ‘Layer Properties Manager’ there is yet another icon of interest. This is the plot icon (a printer). If the printer is displayed it means that the layer will be printed and if the printer is crossed out it means that it wont be.

You may also wish to change the layer on which an item is drawn. For example let us assume that for some reason you wish to change the layer of the hidden lines from ‘Hidden’ to ‘Outline’. All you have to do to achieve this is to choose the lines and select the ‘Outline’ layer from the Layer Control list.

Enough of these layers now; all work and no play make Jack a dull boy, so let us get back to some more commands to add to our arsenal!!

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