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layer are really important in Cad
Probably the most important object property to understand well is the layer property. Experienced AutoCAD users use layers all the time and that is why the Object Properties toolbar contains so many layer functions. Good use of layers is the most important aspect of good drawing practice.
The concept of layers is very important in AutoCAD and the correct use of layers can make your drawing much easier to work with. Basically, layers are the computer equivalent of tracing overlays on a drawing board. However, layers are much more powerful because you can have many layers in a single drawing and you can control the visibility, colour and linetype of layers independently. This makes working with very complicated drawings much more efficient. Layers are effectively a way of ordering your drawing. For example, you may need to create a number of construction lines in a drawing which will not form a part of the finished image. You could create a layer called "Construction" and use this for your construction lines. When the drawing is complete, you could simply turn this layer off so that it can't be seen. The beauty is that you could always turn this layer back on at some future time if modifications to the drawing are required. Experienced AutoCAD users will use layers to order their drawings by drawing components. For example, if you were creating a landscape masterplan, you may have layers called "Trees", "Shrubs", "Path" etc. The main reason for this, apart from it being a simple way to control the drawing, is that the different drawing components may need to be printed in different colours, with different linetypes and with different line widths. Layers can be used to control the way objects are displayed on the computer monitor and how they appear when they are printed.
It is a common misapprehension amongst new users that layers can be used to control the visual hierarchy of objects. In other words, if two objects overlap, it seems reasonable to assume that you could cause one object to display "above" another with the use of layers. This layer model is common to illustration software such as CorelDRAW. However, AutoCAD uses a 3 dimensional drawing space where all objects coexist and are positioned in their correct co-ordinate locations. The concept of an object being displayed above or below another, therefore, is not consistent with this logic. In AutoCAD the display of one object in relation to another is determined by the objects place in the drawing database. Objects drawn more recently will display over another if the two objects occupy the same physical space. It is possible to override this effect using the Display Order tools found on the Tools pull-down, Tools
Display OrderOptions. These options are particularly useful to control the display of overlapping solids and solid hatches that are coplanar. The layer of an object has no effect on its display order.
Although you can have many layers in a drawing, you can only draw on one layer at a time. The layer you are drawing on is said to be the current layer. The Object Properties toolbar displays the current layer information. In the illustration above, you can see that layer "0" is the current layer and that both the colour and linetype are set "ByLayer".
When you start a new drawing, AutoCAD has only one layer. This layer is special and is called layer "0" (zero). Layer 0 is special because you cannot change its name or delete it and it has certain properties which we do not need to consider just now. By default layer 0 is assigned the colour white (colour number 7) and the "Continuous" linetype. Layer 0 is always the current layer when you start a new drawing, however, it is bad drawing practice to use layer 0 for normal drawing. The first thing you should do, therefore, when you start a new AutoCAD drawing is to create some new layers.
The concept of layers is very important in AutoCAD and the correct use of layers can make your drawing much easier to work with. Basically, layers are the computer equivalent of tracing overlays on a drawing board. However, layers are much more powerful because you can have many layers in a single drawing and you can control the visibility, colour and linetype of layers independently. This makes working with very complicated drawings much more efficient. Layers are effectively a way of ordering your drawing. For example, you may need to create a number of construction lines in a drawing which will not form a part of the finished image. You could create a layer called "Construction" and use this for your construction lines. When the drawing is complete, you could simply turn this layer off so that it can't be seen. The beauty is that you could always turn this layer back on at some future time if modifications to the drawing are required.
In simple way we can say that if we have to make a complicated diagram then we should use layer command to differentiate the things. for example if u hav to make a design of building then u can make different things in different layers such as windows in different layer, doors in different layer, walls in different layer. etc.
