Orthographic projection and exploded views

A manufacturer needs exact sizes, not a pretty sketch. Orthographic drawings give every measurement needed to make a product.

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Orthographic projection

An orthographic drawing shows an object as separate 2D views, usually the front view, the plan (view from above) and the end view (side view).
In third angle projection, which is usually used in UK schools, the plan is drawn above the front view and the end view seen from the right is drawn to the right of the front view.
The views line up, so heights and widths match across the page. The drawing shows the projection symbol to say which method is used.

Lines and dimensions

Each line type has a meaning:
Sizes are given in millimetres. The unit mm is not written on every dimension.
LineMeaning
Thick continuous lineVisible outlines and edges
Thin dashed lineHidden detail (edges you cannot see from that view)
Thin chain line (long dash, short dash)Centre lines, such as the centre of a hole
Thin line with arrowheadsA dimension (a size)

Scale and exploded views

A scale shows how the drawing size compares with the real size. 1:2 means the drawing is half the real size; 2:1 means it is twice the real size.
An exploded view shows the parts of a product pulled apart along the lines in which they fit together. It shows how the product is assembled and in what order. Exploded views are often drawn in isometric.
Worked example

A table top is 900 mm long. How long is it on a drawing at a scale of 1:10?

  1. 1:10 means the drawing is one tenth of the real size.
  2. 900 ÷ 10 = 90.
  3. So it is drawn 90 mm long.

Answer: 90 mm.

Key idea

Orthographic drawings show front, plan and end views; in third angle projection the plan goes above the front view. Hidden detail uses thin dashed lines; centre lines use chain lines; sizes are in mm. Exploded views show how parts fit together.

Key words
Orthographic projection
A technical drawing showing separate 2D views (front, plan and end) with exact sizes.
Scale
1:2 means the drawing is half the real size; 2:1 means it is twice the real size.
Exploded view
A drawing showing the parts of a product pulled apart along the lines in which they fit together.

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Extra practice

2 more questions

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  1. In first angle projection, where is the plan drawn?

    1. Above the front view
    2. To the left of the front view
    3. Below the front view
    4. On a separate page
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    Answer: Below the front view

    First angle puts the plan below.

  2. What does a thick continuous line show on an orthographic drawing?

    1. Hidden detail
    2. A visible outline or edge
    3. A centre line
    4. A dimension
    Show the answer

    Answer: A visible outline or edge

    Bold lines are visible edges.

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Sources and references

Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.