What type of lines in a sketch show the main portion of the drawing?

In a sketch, construction lines are typically used to define the main portion of the drawing. These lines serve as guides for the overall layout and help in the positioning of other features of the drawing. Construction lines are generally light and temporary, allowing for adjustments to be made easily as the design evolves. They assist in ensuring accuracy and proportion before finalizing the darker, more definitive lines that represent the finished elements of the drawing.

In contrast, centre lines are used to indicate symmetry or to represent the axes of objects, but they do not depict the main features directly. Dimension lines provide measurements and are crucial for conveying size but are not the primary lines that shape the main structure of a drawing. Foundation lines might refer to outlines or bases of structures but are not a standard terminology within the context of the drafting conventions compared to construction lines.

The application of construction lines promotes a clearer and more organized approach to drawing, especially in technical and engineering sketches where precision is essential.