Paper 2 · population mapping techniques
When constructing a proportional circle map to represent town or city populations, which quantity should be made directly proportional to population size, and how is this achieved?
AThe circle's radius, set directly proportional to population, so doubling the population doubles the radius.
BThe circle's area, set proportional to population by making the radius proportional to the square root of the population value.
CThe circle's circumference, set directly proportional to population, so doubling the population doubles the distance around the edge.
DThe circle's diameter, set directly proportional to population, so doubling the population doubles the width across the circle.
Explanation: Circle sizes on a proportional circle map are calculated so that the circle's AREA (not its radius, diameter or circumference) is proportional to the population represented; because the area of a circle is proportional to the square of its radius, the radius itself must be set proportional to the square root of the population value, so that doubling a city's population increases its circle's area proportionally rather than doubling its diameter.
Derived from ZIMSEC Geography Paper 2, November 2003, Q2
