J4

The measurements of the scale drawing are 8 cm by 4 cm. This means that
1 cm represents 2 m. This is the scale used to draw the plan of the field on paper.
When making an accurate scale drawing, state what it is. Do not write any thing on the
accurate diagram except letters marking points, as in your sketch. When asked for some
particular length, the answer you give should be the actual length required and not the
scaled length.
Indicating scale
There are 4 main ways of indicating the scale used.
1. Statement scale: 1 cm represents 100km is a statement of the scale that means 1
cm on the scale drawing represents 100 km on the ground.
2. Linear scale: A line is drawn and then divided into equal divisions, for example,
divisions of 1 cm. see figure below. Against the linear scale the real distance on
the ground is indicated, in this case kilometers. This means 5 cm on the map
400
represent 400 km on the ground, or 1 cm on the map represents = 80 km.
5
3. Ratio form: 1:100 means 1 cm represents 100 cm. The units in the scale in ratio
form must be the same.
4. Representative fraction: (RF): A ratio scale such as 1:1000 may be written as a
1
representative fraction as . The units in the scale must be the same.
1000
One type of scale can be converted to another.
Example
A scale is given in statement form as 1 cm represents 3 km. write this scale in ratio form.
Solution
Scale in ratio form must have the same units. We therefore convert 3 km to centimeters.
3 km = 3 1000 100 = 300 000 cm.
Therefore 1 cm represents 300 000 cm.
In ratio form, the scale is 1:300 000.
Example