What does A-A represent in line type?

A-A signifies a cutting plane, which is characterized by its use in architectural and engineering drawings to illustrate where a section is cut through an object. This notation is crucial because it indicates the location of a cross-section, allowing viewers to understand the interior features of a structure or component that are not visible in the elevation or floor plan views.

Typically, the designation "A-A" implies that there might be a corresponding section view labeled "A" that shows the details of the area cut by that plane. This is a standard practice in technical drawings, providing a clear reference that helps in interpreting the sectional views accurately.

In contrast, the other options relate to different types of lines used in drawings. For instance, objection lines may be used to indicate unwanted areas, leader lines point towards notes or symbols, and dimension lines denote measurements. However, none of these lines carry the same significance of denoting a cutting plane as A-A does. This clarity in representation is vital in effective communication within construction and design processes.