Plain Scale Drawing

Class, let's work through our first example: drawing a simple door to scale. The real door measures 210 cm in height and 90 cm in width. We'll start from these numbers. First, we choose a scale of 1 cm on paper representing 10 cm in real life, so we divide the height by 10: 210 cm ÷ 10 = 21 cm. Doing the same for the width: 90 cm ÷ 10 = 9 cm. These are the dimensions we will draw. On our paper we sketch a rectangle 21 cm tall by 9 cm wide – that is our scale drawing of the door. Here is the final sketch: a simple door shape drawn to the 1 : 10 scale. Notice how the proportions match the real door, just reduced. We've turned real measurements into a manageable drawing by using a clear scale factor.

Everyone, let's work through a real‑world example of scaling a classroom layout. First, note the actual dimensions: the room is 8 metres long and 6 metres wide. Our scale is 1 cm on the drawing equals 20 cm in reality, which we write as a 1 : 20 ratio. To use the scale, we convert the room's measurements to centimetres first: 8 m = 800 cm, 6 m = 600 cm. Divide each real length by the scale factor (20). The drawing length will be 800 cm ÷ 20 = 40 cm, and the width 600 cm ÷ 20 = 30 cm. With those numbers, we can sketch the room on the board: draw a rectangle 40 cm by 30 cm, then add doors and windows in the same proportion. Remember, the key steps are: convert to the same unit, apply the scale factor, and then draw everything proportionally. Any questions before we move on?

Class, let's work through Example 3: designing a market stall using a scale drawing. First, the real stall measures 2 metres by 1.5 metres. We'll use a scale of 1 cm on paper to represent 5 cm in reality, which is a 1 : 5 ratio. The scale factor is calculated as the drawing length divided by the real length, so 1 cm / 5 cm = 0.2. Applying the factor, the stall drawing will be 40 cm by 30 cm. We add details: a roof overhang and a display shelf. I'll sketch the overhang on the whiteboard. Here's the shelf drawn as a smaller rectangle attached to the front wall. Notice how the same scale is kept throughout. Finally, the line shows the boundary of the stall on the ground plan. Any questions before we finish this example?

Let's wrap up what we've learned about scale drawings and see how they fit into real‑world projects here in Kenya. First, remember the key relationship: the drawn length equals the real length divided by the scale factor. This simple formula lets us turn big ideas into manageable sketches. Next, choosing the right scale depends on the space you have and how much detail you need. A larger scale shows more detail but takes up more paper, while a smaller scale fits bigger objects onto a smaller sheet. Finally, think about the examples we discussed: drawing shelters for a community, planning market stalls, or mapping our school grounds. In each case, a proper scale helps us visualize, plan, and communicate ideas clearly.