[size=13.2611px]The Gini coefficient is usually defined
mathematically based on the
Lorenz curve, which plots the proportion of the total income of the population (y axis) that is cumulatively earned by the bottom x% of the population (see diagram). The line at 45 degrees thus represents perfect equality of incomes. The Gini coefficient can then be thought of as the
ratio of the
area that lies between the line of equality and the
Lorenz curve (marked
A in the diagram) over the total area under the line of equality (marked
A and
B in the diagram); i.e., G =
A / (
A +
B). It is also equal to 2
A and to 1 − 2
B due to the fact that
A +
B = 0.5(since the axes scale from 0 to 1).