Dashed line is a mathematical concept, which is a discontinuous line drawn by points or short lines, and is often used for geometric figures or marks. According to the national standard GB/T 4457. 4-2002 Mechanical Drawing Drawing Drawing Line Drawing Rules In technical drawing, there are mainly two kinds of thin dashed lines and thick dashed lines. Thin dashed lines are used to represent invisible edge lines and invisible contour lines, and thick dashed lines are used to represent lines that allow surface treatment.