If there are four quadrants, why do engineering drawings normally talk about only 1st Angle Projection and 3rd Angle Projection?
What happened to the 2nd and 4th quadrants?
It is a simple question, but understanding the answer helps build a much stronger foundation in engineering drawing and orthographic projection.
Before looking at projection methods, we first need to understand how the four quadrants are created.
Imagine two reference planes intersecting each other at 90 degrees:
Together, they divide the space around an object into four regions called quadrants.
| Quadrant | Position relative to HP | Position relative to VP |
|---|---|---|
| 1st Quadrant | Above HP | In front of VP |
| 2nd Quadrant | Above HP | Behind VP |
| 3rd Quadrant | Below HP | Behind VP |
| 4th Quadrant | Below HP | In front of VP |
The quadrant in which the object is considered determines how its orthographic views are projected and arranged.
In First Angle Projection, the object is considered to be in the first quadrant.
The object is positioned between the observer and the projection plane.
This affects where the projected views appear on the engineering drawing.
For example:
This can initially feel counterintuitive, but the arrangement follows directly from the projection method.
First Angle → views appear on the opposite side.
In Third Angle Projection, the object is considered to be in the third quadrant.
Here, the projection plane lies between the observer and the object.
As a result, the views are arranged more intuitively:
Third Angle → views appear on the same corresponding side.
| Feature | 1st Angle | 3rd Angle |
|---|---|---|
| Quadrant | First | Third |
| Object relationship | Object between observer and plane | Plane between observer and object |
| Top view | Below front view | Above front view |
| Right-side view | Left of front view | Right of front view |
| View arrangement | Opposite side | Corresponding side |
| Used for engineering drawings | Yes | Yes |
The important point is not simply memorising where each view goes.
A design engineer should understand why the views appear there.
That understanding becomes valuable when reading production drawings, preparing CAD drawings, checking components or communicating with manufacturing teams.
This is where the concept becomes interesting.
Consider what happens when the reference planes are rotated or unfolded to create a two-dimensional engineering drawing.
In the second and fourth quadrant arrangements, the resulting front and top views can occupy the same region of the drawing.
In practical terms, the views can overlap, making the representation ambiguous and difficult to interpret.
Engineering drawings are meant to communicate geometry clearly.
If two different views occupy the same drawing space, that clarity is lost.
This is the fundamental reason 2nd Angle and 4th Angle Projection are not normally adopted as standard orthographic projection methods for engineering drawings.
By contrast, 1st and 3rd Angle Projection allow the principal views to be arranged clearly and consistently.
International technical-drawing standards formally define orthographic projection methods. ISO 5456-2 specifically addresses orthographic representations, while ISO 128-3:2022 specifies general principles for presenting views, sections and cuts based on those methods.
It may look like a textbook topic.
It isn’t.
Imagine receiving a component drawing from another engineering team.
You see:
Before interpreting the geometry, you need to understand how those views have been projected.
Misreading the projection convention can lead to an incorrect understanding of the component.
That can affect:
Design → Manufacturing → Inspection → Assembly
This is why projection symbols and drawing conventions matter in professional engineering documentation.
ASME Y14.3 similarly establishes requirements for orthographic and pictorial views used on engineering drawing sheets and models.
A common way of learning engineering drawing is:
First Angle = top view below.
Third Angle = top view above.
That may help in an examination.
But it doesn’t necessarily build engineering understanding.
Instead, visualize these three things:
Observer → Object → Projection Plane
Ask:
Once that relationship becomes clear, First Angle and Third Angle Projection become much easier to understand.
Whenever you receive a production drawing, don’t assume the projection method.
Check the projection symbol and drawing convention in the title block before interpreting the views.
That small habit can prevent a large misunderstanding.
There are four quadrants, but they don’t all produce equally practical arrangements for standard orthographic engineering drawings.
1st Angle and 3rd Angle Projection provide clear and consistent arrangements of views.
2nd and 4th Angle Projection can cause views to overlap when the projection planes are unfolded, making them unsuitable for normal engineering-drawing representation.
So the next time someone asks:
“If there are four quadrants, why do we use only 1st and 3rd Angle Projection?”
Visualize the object, observer and projection planes.
That’s where the concept starts making sense.
Second angle projection is generally not used in engineering drawings because, when the reference planes are unfolded, the front view and top view can fall in the same region of the drawing. This can create overlapping views and make the drawing difficult to interpret clearly.
Fourth angle projection is generally avoided for the same practical reason. After projection and unfolding of the reference planes, the principal views can overlap, which reduces clarity and can create ambiguity in technical drawings.
In first angle projection, the object is positioned between the observer and the projection plane, so views are placed on the opposite side of the corresponding feature. In third angle projection, the projection plane is between the observer and the object, so views are placed on the same corresponding side.
A simple way to remember it is:
Engineering drawings commonly use first angle projection and third angle projection. The method used depends on the applicable drawing standard, company practice, customer requirement, and region. The projection symbol in the title block should always be checked before interpreting the drawing.
Orthographic projection standard:
ISO 5456-2 — Orthographic Representations
Technical drawing views and sections:
ISO 128-3:2022 — Views, Sections and Cuts
US engineering drawing reference:
ASME Y14.3 — Orthographic and Pictorial Views
