CAD drawings range from the simplest with a few hundred geometric objects to the most complex ones with millions of geometric objects. To better control the display and plot of geometric objects, CAD have introduced the concept of layer. This way, CAD users can put different geometric objects on different layers and control the color, linetype, lineweight and other properties by customizing the layer properties. The properties of some CAD objects are set bylayer by default and putting those objects on the specific layers will save you time and there is no need to customize them respectively.