Third angle projection is a method for representing a 3D object as a set of flat, 2D views on an engineering drawing. It’s the standard projection system used in the United States and Canada, and it works by placing each view of an object on the same side as the direction you’re looking from. If you look down at an object, the top view appears above the front view. If you look at it from the right, the right-side view appears to the right of the front view. This intuitive layout is what defines third angle projection and separates it from its counterpart, first angle projection.
The Glass Box Concept
The easiest way to understand third angle projection is to imagine placing your object inside a transparent glass box. You look straight at each face of the box, one at a time, and trace the outline of what you see onto the glass. Each tracing becomes one view of your drawing.
Once all six faces have been “traced,” you mentally unfold the glass box so it lies flat. The face you were looking at from above unfolds upward, becoming the top view. The face you saw from the right unfolds to the right, becoming the right-side view. Every view lands exactly where you’d expect it based on the direction you were looking. That’s the core logic: the view appears on the side nearest to the observer.
How the Views Are Arranged
A standard third angle drawing uses three views: the front view, the top view, and the right-side view. The front view sits in the center and acts as the anchor. The top view is placed directly above it, and the right-side view is placed directly to its right.
These views share dimensions with each other in a specific way. The width of the object is common to both the front and top views, so those two views align vertically. The height is common to the front and right-side views, so those align horizontally. The depth is common to the top and right-side views. This shared-dimension system lets you project lines between views to check that features line up correctly, which is a basic but essential part of drafting.
For more complex objects, you can include additional views (left side, bottom, rear) by continuing to unfold the glass box in the same pattern. But three views are sufficient for most parts.
Hidden Lines and Visibility
Not every feature of an object is visible in every view. A hole on the back face, for instance, won’t be seen from the front. Standard practice uses dashed lines to represent any edge or feature hidden from the viewer’s perspective.
Deciding which lines are hidden and which are visible relies on a key principle of third angle projection: the near side of the object is always near the adjacent view. In the top view, the front edge of the object is closest to the front view on the page. In the right-side view, the front face of the object is closest to the front view. This means that when two features overlap in a view, the one closer to the adjacent view is visible, and the one farther away gets drawn as a dashed hidden line. The direction of projection is always vertically downward for a top view, horizontally front-to-back for a front view, and horizontally right-to-left for a right-side view.
Third Angle vs. First Angle Projection
First angle projection arranges the views using the opposite logic. Instead of the view appearing on the same side as the observer, it appears on the far side of the object. If you look down at a part, the top view ends up below the front view. If you look from the right, the right-side view ends up on the left. The object sits between you and the projection plane, rather than the projection plane sitting between you and the object.
Both methods contain identical information. The views themselves look the same. The only difference is where they’re placed on the page. But this difference matters enormously in practice, because reading a first angle drawing as if it were third angle (or vice versa) can lead to manufacturing the wrong part entirely.
Engineers in Europe adopted first angle projection early on, influenced by the descriptive geometry methods developed in France. Engineers in the United States settled on third angle projection, and by World War I it was standard American practice. The two systems persist today. The U.S. and Canada use third angle projection. Most of Europe, Asia, and other regions default to first angle. Some multinational companies use whichever system their client or partner requires, and modern CAD software can switch between the two freely.
The Projection Symbol
Every properly formatted engineering drawing includes a small symbol in or near the title block that tells you which projection system was used. The third angle projection symbol is a truncated cone (imagine a small traffic cone shape) shown in two views: a circular end-on view representing the top of the cone, and a side view of the cone placed next to it. The critical detail is that in the third angle symbol, the pointed (narrow) end of the cone’s side view always faces toward the circular view. This follows the same logic as the projection itself: the narrower end is closer to the viewer, and the view appears on the near side.
There are actually four acceptable orientations of this symbol. The side view of the cone can appear to the left or the right of the circular view. What matters is that the narrow end points toward the circle. If you see the narrow end pointing away from the circle, that indicates first angle projection instead.
Standards and CAD Software
In the United States, third angle projection is governed by ASME Y14.3, titled “Orthographic and Pictorial Views.” This standard, most recently reaffirmed in 2024, defines the requirements for creating orthographic views on engineering drawings and in digital models. If you’re working in a U.S. engineering environment, this is the standard your drawings are expected to follow.
Most CAD programs sold in North America default to third angle projection when generating 2D drawings from 3D models. In SOLIDWORKS, for example, you can check or change the projection type by right-clicking the drawing sheet in the feature manager and opening its properties. A projection type dropdown lets you toggle between third angle and first angle. AutoCAD, Creo, and other platforms have similar settings. If you’re collaborating across regions, verifying this setting before issuing a drawing prevents costly miscommunication.
Why Third Angle Feels Intuitive
The practical advantage of third angle projection is that views appear where most people naturally expect them. The top of the object is shown above the front view. The right side is shown to the right. This spatial relationship mirrors what you’d see if you physically walked around the object and sketched what you saw from each position. For someone learning to read engineering drawings, third angle projection tends to be easier to interpret without training, because the layout matches everyday spatial reasoning. First angle projection requires you to mentally “flip” the relationship, imagining the view landing on the opposite side of the object from where you’re standing.
That said, neither system is technically superior. Both communicate the same geometry with the same precision. The choice between them is a matter of regional convention, and any working engineer should be comfortable reading both.