Lesson 4.1
The Idea of Projection
The conceptual heart of the whole course. How a three-dimensional building becomes flat drawings that lose nothing — by projecting it, straight-on, onto a series of imaginary planes.
Start hereYou can't put a building on paper. Paper is flat; a building has depth. So drawing seems impossible — until you realise you don't draw the building, you draw its shadow on a wall, cast by parallel light.
That's projection. And it's the single idea that makes plans, sections and elevations all the same thing seen from different sides.
01 — The core idea
Flatten without lying
Imagine a building inside a glass box. From each face of the box, you look straight at the building — not from a corner, not in perspective, but dead-on — and trace what you see onto that pane of glass. Each pane catches one true, undistorted view. Then you unfold the box flat. The panes lay out into the standard set of drawings: plan, elevations, section.
Because you looked straight on with parallel sight-lines (this is what “orthographic” means — ortho, right-angled), nothing is foreshortened. A 3-metre wall stays 3 metres on every pane it appears. That's the magic: projection flattens three dimensions to two while keeping every measurement true. Drag through the unfold below.
A building in a glass box
Folded: the three panes wrap around the building, each catching one straight-on view.
Drag through the unfold. The building never changes shape — the panes just lay out flat, every measurement still true.
02 — The three you'll meet
Plan, section, elevation — one family
From 0.1 you already know these three by their questions. Now you can see why they're a family: each is a different pane of the same glass box.
Plan and section involve slicing the building open; elevation just looks at an uncut outer face. But all three are orthographic — straight-on, parallel projection, measurements true. The next four lessons take each in turn.
| Drawing | The pane / cut | Answers |
|---|---|---|
| Plan | Horizontal cut, looking down | How people move through |
| Section | Vertical cut, looking sideways | How it's built; heights |
| Elevation | Outer face, no cut, looking straight on | What the face looks like |
03 — Why this is the heart
Everything else hangs on this
Projection is the spine of technical drawing. Lineweight (Module 1) tells you which projected edges to emphasise. Scale (Module 2) shrinks the true projection to fit paper. Dimensions (Module 3) annotate it. Every drawing convention you'll learn is, underneath, a rule about how to project the building cleanly and read the result. Master this idea and the rest of the course is detail.
A perspective view (Module 6) looks realistic but lies about measurement — far things shrink, parallel lines converge. You could never build from it, because you can't scale a dimension off it reliably. Orthographic projection sacrifices the realism to keep the truth: every line is to scale, every dimension readable. That's why working drawings — the ones a building is actually built from — are always orthographic, and perspectives are reserved for showing clients how a space will feel. Truth for building, realism for persuading. This course teaches you to draw both, and to know which job each does.
10 minutes, a small box
- Find a small box (a matchbox, a phone case). Look at it straight-on from the front — that's an elevation. From directly above — that's a plan view.
- Notice: when you look straight on, the face you see is its true shape. Tilt it and it distorts. Straight-on is the orthographic rule.
- Imagine slicing the box in half and looking at the cut — that's a section. What does it reveal that the outside hid?
- Write one sentence: why can you build from an orthographic drawing but not from a photo?
Key terms — added to the Drawing Atlas
- Orthographic projection
- Projecting a 3D object onto a plane with parallel sight-lines, looking straight-on, so no foreshortening occurs and measurements stay true.
- Projection plane
- The imaginary plane (a “pane of the glass box”) onto which a building's view is projected and traced.
- Glass-box method
- A teaching model: imagine a building in a glass box, trace each straight-on view onto a pane, then unfold the box flat to get plan, section and elevation.
- Foreshortening
- The apparent shrinking of dimensions that recede from the viewer — present in perspective, absent in orthographic projection.
- Working drawing
- A drawing a building is actually constructed from — always orthographic, because every dimension must be reliably scalable.
- Parallel projection
- Projection in which sight-lines stay parallel rather than converging, the basis of orthographic (and paraline) drawing.
Check yourself
3 quick questions — pick an answer to see why.
Q1What does “orthographic” projection mean?
Q2In the glass-box method, plan, section and elevation are…
Q3Why can you build from an orthographic drawing but not from a photo?
- Projection flattens 3D to 2D by looking straight-on (orthographic) and tracing onto imaginary planes.
- Because sight-lines are parallel, nothing foreshortens — every measurement stays true.
- Plan, section and elevation are one family — different panes of the same glass box, unfolded flat.
- Orthographic keeps truth (you can build from it); perspective keeps realism (you persuade with it).
The plan is the pane you look down through. But a plan isn't a view from above — it's a cut. Where exactly is that cut taken, and why does its height change everything?