In isometric drawing, what angle should the horizontal reference lines be drawn?

In isometric drawing, the horizontal reference lines are conventionally drawn at an angle of 30 degrees above the ground line. This angle is essential because it allows for accurately representing dimensions and shapes in a three-dimensional perspective on a two-dimensional plane.

The 30-degree angle creates an effective way to depict the depth and height of objects without losing the clarity of the drawing. This standard approach helps to maintain the isometric projection's uniform scale along the axes, where the x, y, and z-axes are drawn to represent three-dimensional space. In visualizing the object this way, components are proportionally represented, aiding in the understanding of spatial relationships within the drawing.

In contrast, options suggesting other angles do not accurately reflect the conventions of isometric projection, which are designed to clearly depict three-dimensional structures with minimal distortion of proportions.