The ratio Nf/Nd is known as shape factor, where Nf is the

The ratio N_f/N_d is known as shape factor, where N_f is the number of flow lines and N_d is the number of equipotential drops. Flow net is always drawn with a constant b/a ratio, where b and a are distances between two consecutive flow lines and equipotential lines, respectively. Assuming that b/a ratio remains the same, the shape factor of a flow net will change if the

1. upstream and downstream heads are interchanged
2. soil in the flow space is changed
3. dimensions of the flow space are changed
4. head difference causing the flow is changed

The shape factor depends upon the dimension of flow space.