A gradient expressed as "1 in X" means the land rises 1 unit vertically for every X units of horizontal distance. The smaller the value of X, the steeper the gradient, because the same vertical rise occurs over a shorter horizontal distance.
Comparing the four gradients:
Gradient
Horizontal distance per 1 unit rise
Steepness
1 in 134
134 units
Steepest
1 in 153
153 units
1 in 351
351 units
1 in 531
531 units
Gentlest
1 in 134 is the steepest gradient because the land rises 1 unit over just 134 units of horizontal distance, giving the shortest run for the same rise.
When comparing gradients, always remember: the smaller the denominator, the steeper the slope. You can think of it as a fraction - \(\frac{1}{134}\) is the largest fraction among the four, confirming it represents the steepest incline.