Now, it is not about applying different types of lines to objects without any criteria. In fact, as you could see in the names and descriptions of the types of lines in the "Line Type Manager" window, many of the line types have very clear specific purposes in the different areas of the technical drawing. For example, in a civil engineering drawing, the type of line to show gas installations can be very useful. In mechanical drawing, hidden or center lines are constantly used, and so on. The following examples show some types of lines and their use in technical drawing. In fact, the user of Autocad must know for what the different types are used according to the area for which he draws, since they make up an alphabet of lines.