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Chapter 4. Organizing a Drawing with Layers > Controlling Object Behavior

Controlling Object Behavior

In the previous sections, you learned how to control object properties that determine how an object looks when AutoCAD draws it onscreen, or plots it on paper. In this section, you learn how to control object behavior using the Layer Properties Manager. Specifically, you learn how to control object visibility, and to protect objects from accidentally being edited.

Layer Visibility

One handy feature of using layers to organize objects into logical groups is that you can use the Layer Properties Manager to manipulate groups of objects by modifying layer settings. In addition to controlling object colors and linetypes as previously discussed, you can control object visibility. With a simple click of your pointing device, entire groups of objects become invisible on screen, and non-plottable.

AutoCAD allows you to control object display on screen with two features in the Layer Properties Manager. You can turn layers off and on, and you can freeze and thaw layers. In any case, objects that reside on the layer that’s turned off or frozen become invisible and non-plottable. Additionally, a new feature called Plot/Don’t Plot is introduced with AutoCAD 2000, and it allows you to control whether objects appear on a layer plot. This is true even though the objects are visible on screen.

In the next few sections, you learn about the important differences of turning layers off and on, as opposed freezing and thawing, and you are introduced to the new Plot/ Don’t Plot feature.

Turning Layers Off Versus Freezing Layers

When you place objects on a layer, you can control their visibility by turning the layer on and off or by freezing and thawing the layer. When you turn a layer off or freeze the layer, objects that are on the layer become invisible. They do not display on screen, and they do not plot.

Although the end result of making objects invisible by either turning layers off or by freezing layers may seem the same, there is a very important reason why AutoCAD makes both methods available. When a layer is turned off, even though the objects on the layer become invisible, AutoCAD still performs certain zoom and regeneration calculations on the invisible objects. In contrast, when a layer is frozen, AutoCAD does not include the objects on the frozen layer in zoom or regeneration calculations.

By freezing objects, you can dramatically reduce zoom and regeneration times, which improves your productivity. For example, suppose you have a drawing with thousands of objects. If you only need to edit objects that reside on one layer, then you can increase your productivity by freezing the layers on which all other unneeded objects reside. By freezing the layers that have unneeded objects, you eliminate those objects from AutoCAD’s calculations, reducing the time AutoCAD takes for certain zoom and regeneration functions.

So, if freezing layers improves productivity, why not just always freeze layers instead of turning them off? Every time you thaw a layer that had been frozen, it causes AutoCAD to perform a regeneration, also called a regen. (For those who are new to AutoCAD, a regen is often the most frustrating thing a user can experience because the user must sit idly by, unable to do anything, waiting for AutoCAD to complete its regen calculations.) In contrast, turning layers off (or on) does not cause a regen. Therefore, turning layers off makes sense when you typically need to view the objects in your drawing during an editing session, and only want to temporarily make them invisible. In contrast, freezing layers is the proper choice when there are objects you don’t need to view during a lengthy editing session. By freezing them, AutoCAD visually removes the objects from the screen, but no longer includes the objects on the frozen layers in future regens, which can dramatically reduce overall regen times.

In the following exercise, you experience the difference turning layers off versus freezing layers has on the ZOOM EXTENTS command.


Open the drawing 04DWG02. The drawing displays a circle and a square, side-by-side.

From the Object Properties toolbar, from the Layer control drop-down list, choose the light bulb symbol for the Circle layer, as shown in Figure 4.14, then pick any spot in the drawing. AutoCAD turns the Circle layer off, and removes the circle from the screen.

Figure 4.14. Choosing the light bulb symbol from the Layer drop-down list in the Object Properties toolbar turns off the Circle layer.

At the Command prompt, type Z , then type E . AutoCAD starts the ZOOM command, then executes the Extents option, resulting in the display shown in Figure 4.15.

Figure 4.15. With the Circle layer turned off, AutoCAD calculates the position of the invisible circle when a ZOOM EXTENTS is executed.

From the Object Properties toolbar, from the Layer control drop-down list, choose the sun symbol for the Circle layer, as shown in Figure 4.16, then pick any spot in the drawing. AutoCAD freezes the Circle layer off.

Figure 4.16. Choosing the sun symbol from the Layer drop-down list in the Object Properties toolbar freezes the Circle layer.

At the Command prompt, type Z , then E . AutoCAD starts the ZOOM command, then executes a ZOOM EXTENTS.

Notice now that after AutoCAD performs a ZOOM EXTENTS, the rectangle displays in the center of the screen, as shown in Figure 4.17. By comparing Figures 4.15 and 4.17, you can see the different effect turning a layer off versus freezing the same layer has when performing a ZOOM EXTENTS. When the layer is turned off, AutoCAD still takes the time to calculate the position of the circle. When the layer is frozen, AutoCAD ignores the circle, and only calculates the position of the square.

Figure 4.17. With the Circle layer frozen, AutoCAD does not calculate the position of the invisible circle when a ZOOM EXTENTS is executed.

Although the difference in regen time initiated by the ZOOM EXTENTS was probably imperceptible, the time difference becomes much more obvious when the frozen layer contains thousands of objects.

When finished, you may close the drawing without saving your changes.

Freezing Globally Versus Freezing in the Active Viewport

In the previous section, you learned about the differences between turning off layers and freezing layers. Though the exercise didn’t discuss it, the methods used to turn off and freeze layers were global. In other words, they affect all objects in all viewports. Although turning off or freezing layers in all viewports is generally acceptable, there are circumstances when it is not. Specifically, when you are working with paper space layouts that have multiple viewports, you may want objects on a layer to be visible in one viewport, but invisible in another. This effect is accomplished by freezing layers in the active viewport. For detailed information on freezing layers in the active viewport, see Chapter 19, “Paper Space Layouts.”

The New Plot/Don’t Plot Feature

AutoCAD 2000 introduces a new and very useful feature in the Layer Properties Manager: The Plot/Don’t Plot toggle. This feature controls whether objects on a layer are plotted by toggling the feature on or off. What makes this feature useful is that objects that are visible on screen are prevented from plotting if the Plot/Don’t Plot feature is toggled off. Therefore, you can display and use objects such as construction lines on screen, but prevent them from plotting on paper.


You can use AutoCAD’s Plot Preview feature to view the results of layers set to not plot. For more information, see Chapter 20.


In previous releases, you could simulate the Plot/Don’t Plot feature by creating a layer called DEFPOINTS, and placing objects on it that you wanted to view and edit on screen, but did not want to plot. The problem with this technique was that you could only have one DEFPOINTS layer, and therefore the layer could become cluttered with an array of objects that you needed to use on screen, but did not want to plot.

The Plot/Don’t Plot feature affects blocks and external references (xrefs) in unique ways. For example, you can control which objects in a block won’t plot by setting their layers to not plot. Also, you can prevent an entire block from plotting by setting the layer on which the block is inserted to not plot. This is true for xrefs, as well. Therefore, you can control whether entire blocks and xrefs plot, or you can control whether specific objects in blocks and xrefs plot. For more information, refer to Chapter 20.

Locking Layers

When editing a drawing with multiple layers, you probably will mistakenly select objects that you don’t want to edit. Although this is frustrating, the good news is that you can control which objects are editable by locking and unlocking the layers on which they reside. The ability to lock layers enables you to display the objects on a layer without selecting any objects on that layer. More importantly, although objects on a locked layer are not selectable for edit commands, they can be snapped to using object snaps.

Therefore, the layer locking feature is most useful when working on drawings in which you simply need to see the objects on a layer for reference and object snapping purposes, and you want to ensure that you don’t accidentally alter the objects. By locking a layer, you ensure that the objects on that layer are safe from unintended edits.


You can place blocks on a layer that is locked and even though they may contain data from other layers, you will not be able to erase the blocks.


You can create data on a locked layer and then be unable to modify the same object just created. This can often be a trap during lisp routines creating data but on locked layers.

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