Property
To correctly represent a fraction visually, the whole shape must be divided into parts of equal size. If the parts are not equal, the shaded area does not accurately represent the fraction.
Examples
A circle cut into two pieces, one big and one small, does NOT correctly show 21.
A rectangle divided into 3 strips of different widths does NOT correctly show 31.
To correctly show 41, a square must be divided into four smaller squares of the exact same size.
Explanation
Imagine sharing a pizza. You can't give your friend a tiny sliver and keep the giant rest while calling it 'half'! For fractions to be fair and accurate, every single piece you divide the shape into must be exactly the same size. No cheating by making some parts bigger!