Graphic Representation and Technical Drawing for Design
This domain assesses sketching, projection systems, scale, dimensioning, and the visual presentation of a design proposal. You must communicate a three-dimensional object clearly and correctly, using conventions that another person can read and build from.
Projection and views
Orthographic projection represents an object through separate views: front, top, and side. First-angle and third-angle differ in view placement; Spain commonly uses first-angle in technical drawing, while the symbol on the sheet should make the system explicit. Hidden edges use dashed lines; centre lines use long-short dashes. Isometric projection shows three axes at 120 degrees with true lengths along the axes; cavalier and cabinet are oblique projections. Perspective uses vanishing points and gives a realistic view but is not a working drawing.
Scale and dimensioning
Scale = drawing size : real size. At 1:20, 1 cm on paper equals 20 cm real; at 1:5, 1 cm equals 5 cm. Always state the scale. Dimension lines are thin, with arrowheads or oblique strokes, placed outside the outline where possible. Give overall dimensions and key functional dimensions, not every repeated measurement. Use millimetres in technical drawings unless another unit is stated. Avoid crossing dimension lines; group related dimensions.
Presentation
A proposal sheet usually combines a title, concept statement, orthographic views, an isometric or perspective, a materials key, and dimensions. Keep line weights consistent: thick outlines, medium visible edges, thin dimension and construction lines. Annotate with leaders rather than long paragraphs.
Worked example
Draw a bench 1,800 mm long, 450 mm deep, and 450 mm seat height at 1:20. On paper: 90 mm long, 22.5 mm deep, 22.5 mm seat height. Draw front and side views aligned, add a top view, and include a dashed line for the hidden frame rail. Dimension overall length, seat height, and seat depth. Add an isometric at 1:20 to show the slats. Reasoning: 1:20 fits an A3 sheet and keeps the full object readable; overall dimensions are essential, while repeated slat spacing can be noted once. The isometric explains construction that orthographic views alone may obscure.
Traps
Do not omit the scale or mix units. Do not dimension to hidden or unclear edges. Do not use perspective for manufacturing information. Do not let line weights collapse so that outlines, hidden lines, and dimensions look identical. Check view alignment and projection symbol.