Proportion & Scale
Drawing in proportion and representing scale in perspective drawing is something that takes time and practice. Neither of the two can be effectively measured using a ruler as both proportion and scale within the drawing constantly recedes vertically and horizontally relative to the vanishing planes. To overcome this, you must learn to visually judge or guess an initial measurement to base your drawing on. The judgement of proportion and scale in design drawings should always be based on one factor – human scale.
Drawing by guessing may seem strange to many students of design at first because of the way drawing is taught in the early years of schooling, that is that everything must be measured, ruled precise and absolute. As a designer, it is vital that you begin to learn how to trust your eyes, how to estimate distances and understand that products and environments must be designed for the beings who are intended for its use, or in other words, design the product or environment using human (or other intended being's) proportions to ensure it is functional.
Drawing Using Human Proportion
To draw using human proportion and scale in perspective drawing it is first important to decide on a spatial unit; in the case of environments and most products the average height of a human being is best, approximately 1500mm or 1.5m. In the case of product drawings, choose a measurement that best represents the part of the human body that will use the product you are designing.
Designing to the measurement of 1500mm has distinct advantages for design drawing as it corresponds to the approximate heights of environments and products humans interact with. For example, the average height of ceiling is 3m, desk tops 750mm, chair seats 375mm, and coffee tables 162mm.
To begin your drawing, sketch in the vertical vanishing planes and the horizontal vanishing plane. (Remember, for a more interesting and dynamic view move one or both vanishing point off the page). Draw a vertical line down from the horizontal place to reference the vertical height of a human being - 1500mm or 1.5m. Extend the vertical line an equal distance above the Horizontal Line.
Trace each end of the vertical line back to both vanishing points.
Estimate a depth of 1.5m on one of the vertical planes and draw a vertical line to make the shape of a rectangular box. Remember that you must foreshorten the depth, that is, make it look shorter than what it actually is. Section the bottom half of the rectangle by drawing diagonal lines from one corner of the box to the other. These two diagonal lines can now be used to find the Vanishing Points (VP) for the parallel set of diagonal lines on the Vertical Line (VL).
A shortcut to find the subsequent spatial unit, project a diagonal line down far the top left corner of the rectangular box. Where this line crosses the bottom of the vertical plane you have just drawn, draw a vertical line. This now represents the next spatial unit. What you notice about the space you have just drawn?
This method of dissecting special units can be used in any framework of perspective. However, there are exceptions to its effectiveness when used in particular circumstances.
When drawing very shallow perspective sketches, the depth of the spatial unit can be made on a vertical plane close to the Vanishing Line without too much distortion.
When drawing deeper or wider perspectives, the spatial unit should be made a plane as far out and forward of the Vanishing Line as possible.
Deep or wide perspectives that decide on the spatial unit close to the Vanishing Line and then extended out will result in distortion.
The perspective sketch can then be developed slowly and detail added.