Lines are very important in technical, engineering, and architectural drawings because they give a visual illustration of the sizes and shapes of drawn objects. There are as many as 20 types of drawing lines that have one characteristic or another—or they may even have combined characteristics.
The five main characteristics of lines are as follows:
1. Straight line: A line is straight if it is not bent or doesn’t have any deviation, regardless of its dimension or length. A straight line may be horizontal or vertical, such as the two different lines (A–B) shown in Figure 1. A straight line may also be inclined or not located on the true horizontal or vertical axis.
Figure 1: A horizontal straight line and a vertical straight line
2. Curved line: A line is curved if it takes the shape of an arc and has a radius from a center. Alternatively, a line that is curved may take on an irregular curved shape which doesn’t have a defined radius (see Figure 2).
Figure 2: An arc and an irregular curve
3. Intersecting lines: Intersecting lines are two or more lines that intersect at a point as shown in Figure 3. Usually, the opposite angles of two intersecting lines are equal: a equals a and b equals b as shown in Figure 3.
Figure 3: Intersecting lines
4. Parallel lines: A line is parallel to another line or lines are parallel to each if they are equidistant from each other throughout their length and do not intersect or cross each other (see Figure 4).
Figure 4: Parallel lines
5. Perpendicular lines: A line is perpendicular to another line or lines are perpendicular to each if they intersect each other at an angle of 90° as shown in Figure 5.
Figure 5: Perpendicular lines
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