Write both parts of the scale with the same units, using the smaller units (cm). Convert km to cm by multiplying by 1000 then multiplying by 100. 2 km is the same as 200,000 cm. The scale is 5 cm ...

A measurement-based scale, eg where 1 cm represents 50 km. A ratio scale in the form 1 : 𝑛, eg the ratio 1 : 30,000 means that every centimetre on the map represents 30,000 cm in real life.