Every object has a
? They give you a way to turn groups of objects on and off — both on the screen and on the plot.
? They provide the best way of controlling object color, linetype, and lineweight.
If you spent any time “on the boards,” as grizzled old-timers like to call paper-and-pencil drafting, you may be familiar with the manual drafting equivalent of layers. In
If you’re too young to remember pin-bar drafting — or old enough to prefer not to — you may remember something similar from a textbook about human anatomy. There’s the skeleton on one sheet, the muscles on the next sheet that you laid over the skeleton, and so on until you built up a complete picture of the human body — that is, if your parents didn’t remove some of the more grown-up sections.
CAD layers serve a similar purpose; they enable you to turn on or off groups of related objects. But layers do a lot more. You use them in AutoCAD to control other object display and plot properties, such as color, linetype, and lineweight. You also can use them to make some editing tasks more efficient and reduce the time that it takes AutoCAD to load some drawings. Take the time to give each of your drawings a suitably layered look.
You create layers, assign them names, assign them properties such as color and linetype, and then put objects on them. When you draw an object, AutoCAD automatically puts it on the
Before you draw any object in AutoCAD, you should set an appropriate layer current — creating it first, if necessary, using the procedure described later in this section. If the layer already exists in your drawing, you can make it the current layer by choosing it in the Layers toolbar, as shown in Figure 4-2.
Figure 4-2: Set a current layer before you draw.
Make sure that no objects are selected before you use the Layer drop-down list to change the current layer. (Press the Esc key twice to be sure.) If objects are selected, the Layer drop-down list displays — and lets you change — those objects’ layer. When no objects are selected, the Layer drop-down list displays — and lets you change — the current layer.
If you forget to set an appropriate layer before you draw an object, you can select the object and then change its layer by using either the Properties palette or the Layer drop-down list.
How do you decide what to call your layers and which objects to put on them? Some industries have developed layer guidelines, and many offices have created documented layer standards. Some projects even impose specific layer requirements. (But be careful; if someone says, “You need a brick layer for this project,” that can mean a couple of different things.) Ask experienced CAD drafters in your office or industry how they use layers in AutoCAD. If you can’t find any definitive answer, create a chart of layers for yourself. Each row in the chart should list the layer name, default color, default linetype, default lineweight, and what kinds of objects belong on that layer. Chapter 15 includes an example.
Besides layers, the remaining object properties that you’re likely to want to use often are color, linetype, lineweight, and possibly plot style. Table 4-1 summarizes these four properties.
Table 4-1 Useful Object Properties
| Property | Controls |
|---|---|
| Color | Displayed color and plotted color or lineweight |
| Linetype | Displayed and plotted dash-dot line pattern |
| Lineweight | Displayed and plotted line width |
| Plot style | Plotted characteristics (see Chapter 12) |
In Release 14 and older versions of AutoCAD, color also controlled the plotted lineweight of each object — strange, but now very common in the AutoCAD world. You may find yourself working this way even in AutoCAD 2005, for compatibility with drawings (and co-workers) that use the old way, as described in the “About colors and lineweights” sidebar.
AutoCAD gives you two different ways of controlling object properties:
? By layer: Each layer has a default color, linetype, lineweight, and plot style property. Unless you tell AutoCAD otherwise, objects inherit the properties of the layers on which they’re created. AutoCAD calls this approach controlling properties
? By object: AutoCAD also enables you to override an object’s layer’s property setting and give the object a specific color, linetype, lineweight, or plot style that differs from the layer’s. AutoCAD calls this approach controlling properties
If you’ve worked with other graphics programs, you may be used to assigning properties such as color to specific objects. If so, you’ll be tempted to use the by object approach to assigning properties in AutoCAD. Resist the temptation. In almost all cases, it’s better to create layers, assign properties to each layer, and let the objects on each layer inherit that layer’s properties. Here are some benefits of using the by layer approach:
? You can easily change the properties of a group of related objects that you put on one layer. You simply change the property for the layer, not for a bunch of separate objects.
? Experienced drafters use the by layer approach, so if you work with drawings from other people, you’ll be much more compatible with them if you do it the same way. You’ll also avoid getting yelled at by irate CAD managers, whose jobs include haranguing any hapless newbies who assign properties by object.
AutoCAD drafters traditionally have achieved different printed lineweights by mapping various on-screen display colors of drawing objects to different plotted lineweights. An AutoCAD-using company may decide that red
