You are always drawing on a layer. It may be the default layer or a layer you create and name yourself. Each layer has an associated color and linetype among other properties. For example, you can create a layer on which you draw only centerlines and assign the color blue and the linetype CENTER to that layer. Then, whenever you want to draw centerlines you can switch to that layer and start drawing.
用户总是在图层上绘制图形。可能是默认的图层，也可能是用户自己创建和命名的图层。每个图层都有关联的颜色和线型。例如，可以创建一个图层，在该图层上仅绘制中心线，并将图层颜色指定为蓝色，将图层线型指定为 CENTER。以后每次绘制中心线时，都可以切换到该图层再开始绘制。
All layers and linetypes are stored in separate symbol tables. Layers are kept within the Layers table, and linetypes are kept within the Linetypes table.
所有图层和线型都保存在分开的符号表中。图层保存在层表的内部，线型保存线型表内部。
For more information about working with layers, see “Work with Layers” in the AutoCAD User's Guide.
更多关于操作图层的详细信息，请参见《AutoCAD 用户手册》中的“操作图层”。
